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Old 03-18-2017, 02:42 PM   #1
ShinyC10
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Alternator

1986 c10 p/u

I have attatched a few pictures below. The wiring diagram is my setup no down to the T with exception of the BATT connection. I have a single 4g wire going from BATT to a 40amp maxi fuse and to the jblock. Recently, that 40amp maxi fuse blew and keeps blowing fuses every time I turn the truck on. The initial problem was the BATT stud was somewhat loose on the inside of the case so I opened it up and replace it with another stud from and old alt. The seemed to fix the problem till I drove it then it blew the fuse again. Got back home, popped the hood and put another fuse in and ran a few tests (remaining pictures in the post) and all of them show way higher numbers than what I wanted. Next step, I did a short test with a test light. Took all the fuses out and nothing seemed to be shorted out till I pulled the power accessory circuit breaker (little metal like fuse on the top right of the fuse box). That seemed to turn the test light off. I'm at a loss and need some insight.
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Old 03-20-2017, 12:08 AM   #2
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Re: Alternator

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Originally Posted by ShinyC10 View Post
1986 c10 p/u

I have attatched a few pictures below. The wiring diagram is my setup no down to the T with exception of the BATT connection. I have a single 4g wire going from BATT to a 40amp maxi fuse and to the jblock. Recently, that 40amp maxi fuse blew and keeps blowing fuses every time I turn the truck on. The initial problem was the BATT stud was somewhat loose on the inside of the case so I opened it up and replace it with another stud from and old alt. The seemed to fix the problem till I drove it then it blew the fuse again. Got back home, popped the hood and put another fuse in and ran a few tests (remaining pictures in the post) and all of them show way higher numbers than what I wanted. Next step, I did a short test with a test light. Took all the fuses out and nothing seemed to be shorted out till I pulled the power accessory circuit breaker (little metal like fuse on the top right of the fuse box). That seemed to turn the test light off. I'm at a loss and need some insight.
Well no replies yet so let me see if we can unravel this mystery. I quoted your post so I can bold the things I have questions about.

1. How are you getting power to the cab I assume off the J block since you only have 1, 4 gauge wire from the alternator. Same with the 8 gauge wire off the starter solenoid which also serves as the battery charging wire.

2. Does this mean that you blow the fuse just by turning the key on or does the truck have to be running. This is important to know, because if it's blowing just by turning the key on, it means that the circuit is shorted .

It also figures that the circuit is not shorted, because it is hot without the key on, so it would blow the fuse anytime the battery was connected.

3. If it's blowing while the truck is running, Which I suspect, it means that the maxi-fuse cannot handle the amp surge draw when the electrical loads kick in, and you may need to replace it with a rated fusible link like the one shown in the diagram.

You really don't know if the BATT stud on the alternator was shorted to the case (ground), before you fixed it. Do a continuity check on it and wiggle it around while you are checking it because the engine motion and vibration could cause it to short to ground while it was running.

While we're here you should check all the power wires to be sure they can't touch grounds while the engine is running and if the insulation is good on them. Example: any wire or cable that could be touching the exhaust.

Your two tests with the voltmeter are not much help because they only show voltage drops on the two wires you tested, and .2 volts is not much. Also were they taken with the engine running or Key off or key on.

The best thing you could do is put an amp meter on the alternator output line, and see how many amps are going to the maxi-fuse with the engine running at about 2K, while you turn on the accessories.

4. I'm guessing that the power accessory CB is not a factor because it probably doesn't come into play until your relays are closed by being switched on. How did you check it? engine on or off. Key on or off.

5. Another thing, did the engine die when the fuse blew or did you just see that the alternator quit charging. It would have quit charging when the MF blew but if you had a huge draw on the battery it would have blown the fusible link in the battery feed wire to the J block.

This leads me to believe that the alternator might still be shorting.

That's about all I've got until until I hear more from you.
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Old 03-20-2017, 01:21 AM   #3
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Re: Alternator

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Well no replies yet so let me see if we can unravel this mystery. I quoted your post so I can bold the things I have questions about.

1. How are you getting power to the cab I assume off the J block since you only have 1, 4 gauge wire from the alternator. Same with the 8 gauge wire off the starter solenoid which also serves as the battery charging wire.

2. Does this mean that you blow the fuse just by turning the key on or does the truck have to be running. This is important to know, because if it's blowing just by turning the key on, it means that the circuit is shorted .

It also figures that the circuit is not shorted, because it is hot without the key on, so it would blow the fuse anytime the battery was connected.

3. If it's blowing while the truck is running, Which I suspect, it means that the maxi-fuse cannot handle the amp surge draw when the electrical loads kick in, and you may need to replace it with a rated fusible link like the one shown in the diagram.

You really don't know if the BATT stud on the alternator was shorted to the case (ground), before you fixed it. Do a continuity check on it and wiggle it around while you are checking it because the engine motion and vibration could cause it to short to ground while it was running.

While we're here you should check all the power wires to be sure they can't touch grounds while the engine is running and if the insulation is good on them. Example: any wire or cable that could be touching the exhaust.

Your two tests with the voltmeter are not much help because they only show voltage drops on the two wires you tested, and .2 volts is not much. Also were they taken with the engine running or Key off or key on.

The best thing you could do is put an amp meter on the alternator output line, and see how many amps are going to the maxi-fuse with the engine running at about 2K, while you turn on the accessories.

4. I'm guessing that the power accessory CB is not a factor because it probably doesn't come into play until your relays are closed by being switched on. How did you check it? engine on or off. Key on or off.

5. Another thing, did the engine die when the fuse blew or did you just see that the alternator quit charging. It would have quit charging when the MF blew but if you had a huge draw on the battery it would have blown the fusible link in the battery feed wire to the J block.

This leads me to believe that the alternator might still be shorting.

That's about all I've got until until I hear more from you.
Thanks for the reply Vette. Ill list off my answers with their questions you have.
1. You are correct with your assumption. The power for the cab is coming from the jblock.

2a. Initially, the fuse would blow right when i started the truck. But i figured it was the connection at the BATT stud shorting from a loose connection or the stud itself being loose. I replaced the stud and it seemed to fix the fuse blowing on start up. Then i put it in drive took off down the road and looked at my voltage gauge and it was reading way low. Come to find out the fuse blew.

3. From my previous thread, i believe you helped me with, you suggested the 40amp maxi fuse. it's been running perfectly well since then. I have tried the fusible link setup but it seems to get hot quick. Thats why i have the 4g with the maxi.

The tests from my OP arent showing the numbers that i received. My numbers were coming out to 2x what they show.
Alt BATT stud to battery + = .2
Alt case to battery - = .4
Sense term to battery + = .3
4. I checked the accessory CB with key off. Positive cable removed and the test light in between the cable and the post.

5.The engine continued to run whenever the fuse blew. The voltage just dropped.
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Old 03-20-2017, 02:29 PM   #4
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Re: Alternator

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Thanks for the reply Vette. Ill list off my answers with their questions you have.
1. You are correct with your assumption. The power for the cab is coming from the jblock.

2a. Initially, the fuse would blow right when i started the truck. But i figured it was the connection at the BATT stud shorting from a loose connection or the stud itself being loose. I replaced the stud and it seemed to fix the fuse blowing on start up. Then i put it in drive took off down the road and looked at my voltage gauge and it was reading way low. Come to find out the fuse blew.

3. From my previous thread, i believe you helped me with, you suggested the 40amp maxi fuse. it's been running perfectly well since then. I have tried the fusible link setup but it seems to get hot quick. Thats why i have the 4g with the maxi.

The tests from my OP arent showing the numbers that i received. My numbers were coming out to 2x what they show.
Alt BATT stud to battery + = .2
Alt case to battery - = .4
Sense term to battery + = .3
4. I checked the accessory CB with key off. Positive cable removed and the test light in between the cable and the post.

5.The engine continued to run whenever the fuse blew. The voltage just dropped.
I tend to agree with you that the alternator stud was what blew the fuse and it may still be the culprit. You may have damaged the diode pack in the alternator which could provide a short to ground in the alternator output circuit.

I say this because you have not had major damage out of the battery supply circuit after the fuse blew, (the engine continued to run but the voltage dropped). Obviously the voltage will drop after the alternator quits charging, but the thing to note is that the fusible link didn't melt after the alternator was out of the picture. I would take a voltage reading on the alternator output and make sure it wasn't overcharging and also that none of the diodes were shorted out.

Based on what you've said, I think you've isolated the problem to the alternator. I'm not sure that Autozone or any of the other auto parts stores could test it and determine that it was bad. It should show up as overcharging or shorting with their equipment and the test is free so it might be worth the effort.
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Old 03-20-2017, 02:58 PM   #5
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Re: Alternator

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Originally Posted by VetteVet View Post
I tend to agree with you that the alternator stud was what blew the fuse and it may still be the culprit. You may have damaged the diode pack in the alternator which could provide a short to ground in the alternator output circuit.

I say this because you have not had major damage out of the battery supply circuit after the fuse blew, (the engine continued to run but the voltage dropped). Obviously the voltage will drop after the alternator quits charging, but the thing to note is that the fusible link didn't melt after the alternator was out of the picture. I would take a voltage reading on the alternator output and make sure it wasn't overcharging and also that none of the diodes were shorted out.

Based on what you've said, I think you've isolated the problem to the alternator. I'm not sure that Autozone or any of the other auto parts stores could test it and determine that it was bad. It should show up as overcharging or shorting with their equipment and the test is free so it might be worth the effort.

Thanks again for responding,
I took the alt to orielly's to have it tested but they didn't know how to test it. The alt is a 140a Summitracing brand and it has no part number on it so they didn't know how to run the test. he said that since it didn't come with the truck that the system wouldn't know how to test it. That's what he told me.

As for the diodes, I know they sell rebuild kits for alts but where would I get one for a 140amp? On another thread someone listed a link in their post but it was for like a 60 and 90 amp alt
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Old 03-20-2017, 06:08 PM   #6
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Re: Alternator

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Thanks again for responding,
I took the alt to orielly's to have it tested but they didn't know how to test it. The alt is a 140a Summitracing brand and it has no part number on it so they didn't know how to run the test. he said that since it didn't come with the truck that the system wouldn't know how to test it. That's what he told me.

As for the diodes, I know they sell rebuild kits for alts but where would I get one for a 140amp? On another thread someone listed a link in their post but it was for like a 60 and 90 amp alt

Quote:
I'm not sure that Autozone or any of the other auto parts stores could test it and determine that it was bad. It should show up as overcharging or shorting with their equipment and the test is free so it might be worth the effort. Quoted myself
Point, set, match.

How long have you had the alternator? Maybe you could get Summit to exchange it for you. If not you might find a shop in your area that rebuilds them. If it were me I think I would go with a CS 144, and wire in a resistor in the exciter wire. How much amperage do you need? 90 amps would be a good swap in test alternator, to see if the problem persists. Then if it runs OK, then you could upgrade to the CS or replace the summit 140 amp. Course if it's chromed then you have to have the bling.

Is that the one for $250?

Summit lists repair kits for powermaster 140 amp alternators.
https://www.summitracing.com/search?...0repair%20kits.



I did a little googling for you.


https://www.google.com/webhp?sourcei...,lf:1,lf_ui:10
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Old 03-20-2017, 08:21 PM   #7
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Re: Alternator

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Point, set, match.

How long have you had the alternator? Maybe you could get Summit to exchange it for you. If not you might find a shop in your area that rebuilds them. If it were me I think I would go with a CS 144, and wire in a resistor in the exciter wire. How much amperage do you need? 90 amps would be a good swap in test alternator, to see if the problem persists. Then if it runs OK, then you could upgrade to the CS or replace the summit 140 amp. Course if it's chromed then you have to have the bling.

Is that the one for $250?

Summit lists repair kits for powermaster 140 amp alternators.
https://www.summitracing.com/search?...0repair%20kits.



I did a little googling for you.


https://www.google.com/webhp?sourcei...,lf:1,lf_ui:10


I still have warranty on it I believe. Just didn't want to go trough paying for shipping and turns out it's totally okay. And no it's the one for 140ish. Also i did a diode test on my old alternator and my current one and they both came up with the same results: position lead on the BATT stud and negative lead on the case reads nothing. And the negative lead on the stud and the positive on the case reads 10.51

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Old 03-21-2017, 12:32 AM   #8
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Re: Alternator

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I still have warranty on it I believe. Just didn't want to go trough paying for shipping and turns out it's totally okay. And no it's the one for 140ish. Also i did a diode test on my old alternator and my current one and they both came up with the same results: position lead on the BATT stud and negative lead on the case reads nothing. And the negative lead on the stud and the positive on the case reads 10.51
Your test is right and it's not showing the diode pack is grounded to the case.

Did you ever test the output of the alternator when the engine was running before the maxifuse blew? Red lead on the output stud and black lead to case looking for 13 to 15.5 volts.

If you are getting 16 plus then the alternator is overcharging and putting too much current through the MF and causing it to blow.

As long as you're not showing a short to ground through the alternator, I think I would run a bypass wire from the alternator to the junction without the maxifuse, and read the alternator output. Turn on all the accessories that you have and read the meter. I could be that you are simply using too small a Maxifuse or you need the fusible link. Most of our year vehicles do not use a fuse or a fusible link in the charging wire to the junction but everything from the junction is fused.

Yours is newer so they may have started using them when they changed the alternator routing to the starter solenoid.

I have been assuming that your truck has the 12 SI alternator so is that correct?
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Old 03-21-2017, 01:38 AM   #9
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Re: Alternator

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Your test is right and it's not showing the diode pack is grounded to the case.

Did you ever test the output of the alternator when the engine was running before the maxifuse blew? Red lead on the output stud and black lead to case looking for 13 to 15.5 volts.

If you are getting 16 plus then the alternator is overcharging and putting too much current through the MF and causing it to blow.

As long as you're not showing a short to ground through the alternator, I think I would run a bypass wire from the alternator to the junction without the maxifuse, and read the alternator output. Turn on all the accessories that you have and read the meter. I could be that you are simply using too small a Maxifuse or you need the fusible link. Most of our year vehicles do not use a fuse or a fusible link in the charging wire to the junction but everything from the junction is fused.

Yours is newer so they may have started using them when they changed the alternator routing to the starter solenoid.

I have been assuming that your truck has the 12 SI alternator so is that correct?
Yes it is the 12si. And I'll check that stud tomorrow.
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Old 03-21-2017, 10:00 AM   #10
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Re: Alternator

****10si alternator****
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Old 03-24-2017, 07:57 PM   #11
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Re: Alternator

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Your test is right and it's not showing the diode pack is grounded to the case.

Did you ever test the output of the alternator when the engine was running before the maxifuse blew? Red lead on the output stud and black lead to case looking for 13 to 15.5 volts.

If you are getting 16 plus then the alternator is overcharging and putting too much current through the MF and causing it to blow.

As long as you're not showing a short to ground through the alternator, I think I would run a bypass wire from the alternator to the junction without the maxifuse, and read the alternator output. Turn on all the accessories that you have and read the meter. I could be that you are simply using too small a Maxifuse or you need the fusible link. Most of our year vehicles do not use a fuse or a fusible link in the charging wire to the junction but everything from the junction is fused.

Yours is newer so they may have started using them when they changed the alternator routing to the starter solenoid.

I have been assuming that your truck has the 12 SI alternator so is that correct?

Sorry for the late update, hope you're still here.
Got a rebuild kit on the way from summit. In the meantime I put the alt back in with a 40amp maxi fuse and turned the truck on. I also turned the headlights on, driver door open, radio on and ac on and the alt stud was reading 14.06v while those were running. With the truck running with nothing on except the door open the stud was reading just around 14.56v. The one thing that bothers me is that my volt gauge reading drops down to almost 11v with everything on (radio, lights, etc.) all of his is with a 40amp MF
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Old 03-24-2017, 09:11 PM   #12
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Re: Alternator

Maybe off topic but the 1st drawing has the ground to the frame, which is wrong, making the rest of the drawings suspect.
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Old 03-24-2017, 10:54 PM   #13
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Re: Alternator

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Maybe off topic but the 1st drawing has the ground to the frame, which is wrong, making the rest of the drawings suspect.
You're right but he used an illustration with a rear mounted battery, so it would make sense to ground to the frame unless he wanted to run a ground cable back up to the engine. Then he'd have to ground the engine to the frame up front to complete the ground path. I seem to remember a thread with this drawing where the writer had two batteries, one in back and one in front.
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Old 03-24-2017, 11:11 PM   #14
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Re: Alternator

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Maybe off topic but the 1st drawing has the ground to the frame, which is wrong, making the rest of the drawings suspect.
My battery is still grounded the way it is from the factory. The illustration was more focused on the bus bar, starter and alt wiring. Sorry for the confusion
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Old 03-24-2017, 11:16 PM   #15
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Re: Alternator

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Sorry for the late update, hope you're still here.
Got a rebuild kit on the way from summit. In the meantime I put the alt back in with a 40amp maxi fuse and turned the truck on. I also turned the headlights on, driver door open, radio on and ac on and the alt stud was reading 14.06v while those were running. With the truck running with nothing on except the door open the stud was reading just around 14.56v. The one thing that bothers me is that my volt gauge reading drops down to almost 11v with everything on (radio, lights, etc.) all of his is with a 40amp MF
I would try moving the sensing wire over to the green accessory wire connection on the junction. Are your lights dimming at idle?
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Old 03-24-2017, 11:33 PM   #16
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Re: Alternator

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I would try moving the sensing wire over to the green accessory wire connection on the junction. Are your lights dimming at idle?
Not lights don't seem to dim at idle. What would be the differnce in the spot on the junction for the sense wire?
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Old 03-25-2017, 01:00 AM   #17
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Re: Alternator

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Not lights don't seem to dim at idle. What would be the differnce in the spot on the junction for the sense wire?
I was thinking that you might get a better voltage sensing from there, so the alternator could adjust for the voltage drops as you turned on the loads.

if the lights were dimming it means that he alternator isn't keeping up with the amperage draw on the system. You might not notice much dimming at 11 volts though.

Is the MF holding up?
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Old 03-25-2017, 01:18 AM   #18
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Re: Alternator

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I was thinking that you might get a better voltage sensing from there, so the alternator could adjust for the voltage drops as you turned on the loads.

if the lights were dimming it means that he alternator isn't keeping up with the amperage draw on the system. You might not notice much dimming at 11 volts though.

Is the MF holding up?
I didn't drive it but tomorrow I plan to. I just let it idle to see if the MF held up for that but tomorrow I'll find out. And the rebuild kit comes in
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Old 03-25-2017, 09:32 AM   #19
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Re: Alternator

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1986 c10 p/u

The wiring diagram is my setup no down to the T with exception of the BATT connection. I have a single 4g wire going from BATT to a 40amp maxi fuse and to the jblock. Recently, that 40amp maxi fuse blew and keeps blowing fuses every time I turn the truck on. .
Can you clarify something, as my interpretation of what you wrote does not jive with the diagram.

You say with the exception of the BAT terminal. The way I interpret what you've wrote, is there is only a single wire coming off your Bat terminal. Is that correct? Or does it have two wires as the diagram you posted shows?

Because if you have only 1 wire connected, through that 40amp fuse you are way under fused for your alternator. And as Vettevet said, your inrush is likely blowing your fuse. Unless you are taxing your alternator to the limits, a 120 amp maxi fuse should do.

Alex.
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Old 03-25-2017, 12:33 PM   #20
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Re: Alternator

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Can you clarify something, as my interpretation of what you wrote does not jive with the diagram.

You say with the exception of the BAT terminal. The way I interpret what you've wrote, is there is only a single wire coming off your Bat terminal. Is that correct? Or does it have two wires as the diagram you posted shows?

Because if you have only 1 wire connected, through that 40amp fuse you are way under fused for your alternator. And as Vettevet said, your inrush is likely blowing your fuse. Unless you are taxing your alternator to the limits, a 120 amp maxi fuse should do.

Alex.

Yes you are correct, from my 140amp alt Bat stud I have one 4g wire with an inline 40amp maxi fuse to the junction block.
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Old 03-25-2017, 01:01 PM   #21
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Re: Alternator

I addition to my previous post; a 120amp seems kinda large. The biggest one I have near me is an 80amp. I'll have to order a few of them 120s
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Old 03-26-2017, 09:54 AM   #22
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Re: Alternator

80 will hold you over for now. Your 40amp just wasn't enough.
Just don't turn everything on when you start the truck, and let it run for a minute or so to let the alternator just re-charge the battery after starting. The longer it sits between starting, the more important this is as the batteries need more charging and will take a significant draw.

Under ideal circumstances, you would be fused higher than 120. But you would also be running a heavier wire from the battery direct to the alternator output (fused).
Consider the 120 amp to fuse the 4 guage wire, and not be stressed by your load. I will say, don't let this get you all concerned at this point, unless you start really putting a serious load on the system. If you are mostly stock at this point you probably won't run into any issues. And with LED lighting, I'd go so far as to say if you do go crazy with adding flood lights, LED's are not going to put you in the danger zone like a couple sets of old incandescent lights would.

What you do want to do is get your hands on a clamp on DC ammeter so you can verify what kind of current the truck is drawing after a start. And what kind of current it is drawing when you have everything turned on. Both for peace of mind, and verifying something else is not wrong.

Alex.
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Old 03-26-2017, 12:38 PM   #23
ShinyC10
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Join Date: Jun 2012
Location: Houston, TX
Posts: 205
Re: Alternator

Quote:
Originally Posted by Axle View Post
80 will hold you over for now. Your 40amp just wasn't enough.
Just don't turn everything on when you start the truck, and let it run for a minute or so to let the alternator just re-charge the battery after starting. The longer it sits between starting, the more important this is as the batteries need more charging and will take a significant draw.

Under ideal circumstances, you would be fused higher than 120. But you would also be running a heavier wire from the battery direct to the alternator output (fused).
Consider the 120 amp to fuse the 4 guage wire, and not be stressed by your load. I will say, don't let this get you all concerned at this point, unless you start really putting a serious load on the system. If you are mostly stock at this point you probably won't run into any issues. And with LED lighting, I'd go so far as to say if you do go crazy with adding flood lights, LED's are not going to put you in the danger zone like a couple sets of old incandescent lights would.

What you do want to do is get your hands on a clamp on DC ammeter so you can verify what kind of current the truck is drawing after a start. And what kind of current it is drawing when you have everything turned on. Both for peace of mind, and verifying something else is not wrong.

Alex.

Sounds good. Thanks for the help guys!
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Old 03-26-2017, 02:31 PM   #24
ShinyC10
Registered User
 
Join Date: Jun 2012
Location: Houston, TX
Posts: 205
Re: Alternator

Quote:
Originally Posted by Axle View Post
80 will hold you over for now. Your 40amp just wasn't enough.
Just don't turn everything on when you start the truck, and let it run for a minute or so to let the alternator just re-charge the battery after starting. The longer it sits between starting, the more important this is as the batteries need more charging and will take a significant draw.

Under ideal circumstances, you would be fused higher than 120. But you would also be running a heavier wire from the battery direct to the alternator output (fused).
Consider the 120 amp to fuse the 4 guage wire, and not be stressed by your load. I will say, don't let this get you all concerned at this point, unless you start really putting a serious load on the system. If you are mostly stock at this point you probably won't run into any issues. And with LED lighting, I'd go so far as to say if you do go crazy with adding flood lights, LED's are not going to put you in the danger zone like a couple sets of old incandescent lights would.

What you do want to do is get your hands on a clamp on DC ammeter so you can verify what kind of current the truck is drawing after a start. And what kind of current it is drawing when you have everything turned on. Both for peace of mind, and verifying something else is not wrong.

Alex.

Sounds good. Thanks for the help guys!
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Old 03-26-2017, 06:12 PM   #25
ShinyC10
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Join Date: Jun 2012
Location: Houston, TX
Posts: 205
Re: Alternator

If you guys are still paying attention to this thread, I put in the rebuild kit for the alt and the diodes still test the exact same as the ones I replaced.

Before alt rebuild kit was put it +lead to the stud and -lead to case read nothing
And with the leads switched it read around 1058 or something.
After putting in the rebuild kit +lead reads on stud and -lead in case reads nothing and with the leads switched it reads around 978. What does that mean?
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