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Old 05-22-2012, 10:43 AM   #1
mrdave03
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65 C10 alternator conversion w/external shunt ammeter?

Ok... I have read all the conversion threads and am confused on one item. My 65 has an external shunt ammeter ( D on left C on right no numbers). No Gen light. If I convert to a 3 wire alt. Will this ammeter provide the needed 10 ohm resistance. Or will I still need to add a bulb or resistor inline for the 10 ohm resistance? It appears the brown wire goes to the dash to the ammeter where trucks with Gen lights it feeds the light.. I think I have the rest figured out but am not sure just splicing the plug wires at the old VR ..the brown wire to the white then white to #1 on alt. Then red to blue and blue to #2 on alt as shown in other threads is enough resistance with it feeding thru the ammeter. If I need to add a bulb or resistor where would the suggested place be to splice it in? Also will the ammeter still function with the new 3 wire alt?
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Old 05-22-2012, 12:59 PM   #2
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Re: 65 C10 alternator conversion w/external shunt ammeter?

The first thing you need to do is get it out of your mind that the ammeter provides the resistance for the alternator to charge. It has nothing to do with whether the alternator charges or not. All it does is read the voltage differential between the voltage at the battery and the voltage at the junction of the alternator feed wire at the end of the shunt wire.

The resistance for the alternator for terminal 1 comes from either the charge light via the brown wire inside the cab to the firewall block, or the resistance wire from the key switch to the same place inside the cab on the firewall block. This is a brown wire with a white stripe and can be clearly seen in the diagram below. Of course you can always wire in a resistor if you don't have either of these options.

Here is the diagram inside the cab and you can see each of the two wires and where they terminate on the firewall block. Look at the ignition switch in the top center of the diagram and the brown/white wire is on the top of the switch. The charging light wire is on the right side of the diagram and it has a tan wire that comes from the light to the same place as the brown/white wire.

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Here is the engine side of the firewall block showing the brown wire going to the external voltage regulator and the jumpers for the conversion.

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The ammeter will still work with the three wire alternator as long as it is wired correctly and the inline fuses are good. There are two wires that go to the ammeter from the charging circuit. One is a black wire that runs from the terminal junction on the passenger fender on the 67 to 72 trucks and I think on the older ones as well.

It will share the junction with the battery positive fusible link wire and the battery end of the shunt. The fuse is a four amp and is in a little football shaped holder. They are sometimes hard to find. The other wire is a black with white stripe and joins the alternator junction with the alternator end of the shunt wire and the wire that feeds the cab circuits.
These two wires run to the firewall connector and then to the dash plug. The shunt and the fuses are in this one.

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Old 05-22-2012, 08:40 PM   #3
ray_mcavoy
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Re: 65 C10 alternator conversion w/external shunt ammeter?

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Originally Posted by VetteVet View Post
The ammeter will still work with the three wire alternator as long as it is wired correctly and the inline fuses are good. There are two wires that go to the ammeter from the charging circuit. One is a black wire that runs from the terminal junction on the passenger fender on the 67 to 72 trucks and I think on the older ones as well.

It will share the junction with the battery positive fusible link wire and the battery end of the shunt. The fuse is a four amp and is in a little football shaped holder. They are sometimes hard to find. The other wire is a black with white stripe and joins the alternator junction with the alternator end of the shunt wire and the wire that feeds the cab circuits.
These two wires run to the firewall connector and then to the dash plug. The shunt and the fuses are in this one.
Just for the record, the ammeter connection points are slightly different on the 64-66 trucks. The black wire goes to the battery post on the starter solenoid since these years don't have the junction block on the fender near the battery like 67-72. And the black w/white stripe wire goes to a buss bar / junction that's part of the horn relay (instead of an internal splice in the harness like 67-72). The 64-66 horn realy is out on the radiator support near the voltage regulator.

I've also found it curious that the 63-66 trucks didn't originally have those small inline fuses in the ammeter wiring like the 61-62 & 67-72 trucks. I don't know why they stopped using them in that time frame ... possibly some sort of ill conceived cost cutting measure. Adding them is a really good idea though. I've seen a number of 63-66 wiring harnesses with melted insulation on the ammeter wiring that was most likely due to an open circuit in the shunt wiring forcing the full current through the meter wiring.

Finally, the 66 & earlier trucks didn't have any fusible links from the factory either. So adding those would be a good idea as well.
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Old 05-23-2012, 12:11 AM   #4
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Re: 65 C10 alternator conversion w/external shunt ammeter?

Thanks for the corrections Ray, I wasn't sure on the older trucks and didn't have any diagrams to go by. my diagrams are all for the charging light which don't have the ammeters.
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Old 05-23-2012, 04:46 AM   #5
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Re: 65 C10 alternator conversion w/external shunt ammeter?

Thank you guys. Exactly the info I was looking for. I thought it wise to add the fusible link near the battery. Also what is the size of the fuses in the ammeter line? I have a much better understanding now.. oh and Ray... do you know if the 64-66 years also had the resistance wire as VetVette states for the 67 and up years?
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Old 05-24-2012, 07:06 PM   #6
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Re: 65 C10 alternator conversion w/external shunt ammeter?

You can use 4 Amp fuses (same as the 67-72 trucks) to add protection to the ammeter circuit.

Yes, 64-66 should have the resistance wire just like VetteVet described for the 67-up trucks. It's even the same color ... brown with a white stripe.

The 2nd diagram that VetteVet posted showing how to jumper the wires at the old voltage regulator plug and how to connect them to the new internally regulated alternator should work just fine on your 65.
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Old 05-25-2012, 04:29 AM   #7
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Re: 65 C10 alternator conversion w/external shunt ammeter?

Fantastic... I'm at ease now doing the swap... just one last question. It shouldn't matter where in the red battery line the fusible link goes correct? The schematic shows on later trucks on the battery end the only issue is the ones sold around here have the ring connector already attached it would be easier to put the ring on he horn relay block...but not sure if location matters. Also websites vary. Some say the link should be two gauges smaller than the wire its protecting.. some say four.. does anyone know the fact on size needed for a 10 gauge wire? link size of 12 or 14?
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Old 05-25-2012, 08:39 AM   #8
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Re: 65 C10 alternator conversion w/external shunt ammeter?

The link is the weak link in the wire (pun intended) so the closer to the power source the better. I think you would be ok putting it on the horn relay. The worst case,you'd have to replace the battery feed wire. The link is 4 gauges smaller than the wire it protects. The confusion comes because the AWG automotive wires are normally classed as even gauge and two wire sizes from 10 to 14 is actually four sizes. The odd sizes are counted but not used. This website from Mad electric explains it better than I can.

http://www.madelectrical.com/catalog/fusible-link.shtml
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Old 07-31-2012, 10:33 AM   #9
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Re: 65 C10 alternator conversion w/external shunt ammeter?

Need a little help with a 71 c10 I recently picked up. It seems to have a painless kit with blade fuses and an internally regulated 3 wire alternator. The 2 wire plug on top of the alternator is not there which is most likely why it's not charging and I'm trying to figure out the connections that need to be made. I'm not real impressed with the install that was done on the re-wire job.
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Old 07-31-2012, 10:44 AM   #10
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Re: 65 C10 alternator conversion w/external shunt ammeter?

(A quick check and I found a diagram that shows that it might not be internally regulated).
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Old 07-31-2012, 11:04 AM   #11
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Re: 65 C10 alternator conversion w/external shunt ammeter?

One wire alternators don't have the plug on top. It still will charge if the large wire on the back is connected to the battery positive either at the battery or down the line where the external voltage regulator red wire goes with the junction with the cab feed wire. Your truck will not have the horn relay on the engine side of the firewall so they used a soldered junction for the four red wires to connect together. See post 2 above.

Just connect a voltmeter to the back of the alternator and to ground and take the reading. If you get over 13.5 to 15 then it's charging.
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Old 07-31-2012, 12:00 PM   #12
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Re: 65 C10 alternator conversion w/external shunt ammeter?

Thx Vet,
I just got the truck and am trying to sort out a number of things including the charging issue.
Went to the muffler shop yesterday and had to jump it to get home. Got home and pulled the battery cable and it quit running. Since it won't run without a battery and the fact it stranded me it's obviously not charging.
Had the alternator tested and it's good - they had to utilize the R and F terminals to test it so it's not a 1 wire.

The hot wire on the back of the alt. is run direct to the battery but there's nothing plugged into the top which is marked R and F.
I suppose the easy way out would be to get a 1 wire but I'd like to keep my chrome alt.

I have a couple more questions:

1. The 71 models don't use a horn relay or does the painless kit eliminate it?
2. Being it's not a 1 wire it will never charge without R and F connected as it currently is?
3. And since it seems to be internally regulated will this simple diagram work? (The color diagram showing the alternator and a diode).

http://www.ytmag.com/cgi-bin/viewit....rtips&th=24290
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Old 07-31-2012, 12:53 PM   #13
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Re: 65 C10 alternator conversion w/external shunt ammeter?

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Thx Vet,
I just got the truck and am trying to sort out a number of things including the charging issue.
Went to the muffler shop yesterday and had to jump it to get home. Got home and pulled the battery cable and it quit running. Since it won't run without a battery and the fact it stranded me it's obviously not charging.
Had the alternator tested and it's good - they had to utilize the R and F terminals to test it so it's not a 1 wire.

The hot wire on the back of the alt. is run direct to the battery but there's nothing plugged into the top which is marked R and F.
I suppose the easy way out would be to get a 1 wire but I'd like to keep my chrome alt.

I have a couple more questions:

1. The 71 models don't use a horn relay or does the painless kit eliminate it?
2. Being it's not a 1 wire it will never charge without R and F connected as it currently is?
3. And since it seems to be internally regulated will this simple diagram work? (The color diagram showing the alternator and a diode).

http://www.ytmag.com/cgi-bin/viewit....rtips&th=24290
1. Look for the horn relay here. It might be over the fuse panel also. Look for a large red and green wire and a smaller black wire in a terminal end that plugs into the relay.

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2. R and F are the terminals used on alternators with the external voltage regulators. The internal alternators use 1 and 2 for the sensing and field terminals. I have seen some external reg alternators with the terminals on the side or top but usually they are on the back. I saw a 71 the other day just like that. How did they hook up the alternator when they tested it? Did they use a regulator or a feed wire to the F terminal? If they used a regulator then you will have to go to that or change the regulator inside the case to an internal one.

3. If it is internally regulated then the picture in the thread you linked will work but You should not need either the diode or a resistor since you will have a charge light or a brown resistance wire from the key switch ( if you have an ammeter) Then you just need to connect the brown wire on the engine side of the firewall to the F terminal and the red wire to the R terminal.
I'll double check that and edit if it is backwards. The normal internal regulated wires would be brown to no.1 and the red to no. 2. Notice that is how this one is wired.

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Old 07-31-2012, 01:10 PM   #14
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Re: 65 C10 alternator conversion w/external shunt ammeter?

I just had a thought about the chrome alternator you have. it may be possible that they took the guts out of the original alternator ( externally regulated ) and chromed the case and then put it back together with the external regulator inside. That's why I asked how they checked it at the store.
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Old 07-31-2012, 01:39 PM   #15
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Re: 65 C10 alternator conversion w/external shunt ammeter?

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Originally Posted by VetteVet View Post
I just had a thought about the chrome alternator you have. it may be possible that they took the guts out of the original alternator ( externally regulated ) and chromed the case and then put it back together with the external regulator inside. That's why I asked how they checked it at the store.
He put it on their machine and spun it and got about 14 volts...had to connect F and R terminals. He said it was internally regulated.
Also, the truck has aftermarket auto meter gauges with a volt gauge so it won't be going through an ammeter.

Was putting in a new battery cable and the bakelite or whatever it is on the starter solenoid was broken and when I touched it it fell apart so I have another issue before I can even try wiring and testing the alternator.
Gotta love those old trucks...
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Old 07-31-2012, 01:40 PM   #16
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Re: 65 C10 alternator conversion w/external shunt ammeter?

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Originally Posted by VetteVet View Post
1. Look for the horn relay here. It might be over the fuse panel also. Look for a large red and green wire and a smaller black wire in a terminal end that plugs into the relay.

Attachment 964198

2. R and F are the terminals used on alternators with the external voltage regulators. The internal alternators use 1 and 2 for the sensing and field terminals. I have seen some external reg alternators with the terminals on the side or top but usually they are on the back. I saw a 71 the other day just like that. How did they hook up the alternator when they tested it? Did they use a regulator or a feed wire to the F terminal? If they used a regulator then you will have to go to that or change the regulator inside the case to an internal one.

3. If it is internally regulated then the picture in the thread you linked will work but You should not need either the diode or a resistor since you will have a charge light or a brown resistance wire from the key switch ( if you have an ammeter) Then you just need to connect the brown wire on the engine side of the firewall to the F terminal and the red wire to the R terminal.
I'll double check that and edit if it is backwards. The normal internal regulated wires would be brown to no.1 and the red to no. 2. Notice that is how this one is wired.

Attachment 964205
Thx for posting the pics. I'll check it out.
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Old 08-01-2012, 06:25 PM   #17
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Re: 65 C10 alternator conversion w/external shunt ammeter?

OK, I finally had time to look into the charging issue. I wired it like the picture in post 13 with a light bulb for resistance and when I pull the battery cable it continues to run so it should be charging. Thanks Vet for your help.
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