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Old 06-27-2013, 04:34 PM   #1
70STOVEBOLT
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Ammeter not working

Ok, I searched but could not find any threads on the problem I am having. I removed my cluster yesterday to replace the dash pad. The ammeter was working fine prior to this. After I reinstall it, the ammeter needle is pointing to discharge side and does not move. What could have gone wrong? 1970 C10
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Old 06-28-2013, 11:49 PM   #2
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Re: Ammeter not working

check the two wires that go to the dash plug to pins 1 and 12 for 12 volts. It sounds like you may have blown one of the 4 amp fuses on the wires or the connections on the pins are not making contact.
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Old 07-01-2013, 10:22 AM   #3
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Re: Ammeter not working

I will check that out. When I bought the truck 11 years ago, the ammeter did not work, but the needle was right on the line, neither charging or discharging. Some years later, I discovered the fuses and replaced them (they were both blown) and it has worked ever since. However, now it is stuck at about "11 o'clock" on the discharge side. I will check the fuses, hopefully that is it. If not, I will check the wires on the cluster feed. On my other problem, with the fuel gauge, the brown wire must've gotten bumped because it was partially unplugged from the fuse block. I pushed it back in all the way and the fuel gauge has been working fine. Thank you for your help vettevet. I will let you know the outcome on this problem.
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Old 07-12-2013, 12:07 PM   #4
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Re: Ammeter not working

Howdy, My ampmeter hasn't worked since I bought the truck. Are the fuses in line or are they in the box? I wouldn't be surprised if the PO pulled the wires completely.
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Old 07-12-2013, 12:24 PM   #5
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Re: Ammeter not working

The fuses are inline in the wiring harness on each side of the radiator on the back side of the core support, black wires. They must use a 4 amp short fuse.
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Old 07-12-2013, 12:26 PM   #6
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Re: Ammeter not working

Update: the ammeter now works, but it still reads on the discharge side, both when the truck is running and when the key is shut off. Is it possible I bumped it somehow to make the needle read off-center?
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Old 07-12-2013, 08:19 PM   #7
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Re: Ammeter not working

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Originally Posted by 70STOVEBOLT View Post
Update: the ammeter now works, but it still reads on the discharge side, both when the truck is running and when the key is shut off. Is it possible I bumped it somehow to make the needle read off-center?
You didn't happen to get the wires crossed up when you changed the fuses, did you. That would cause the ammeter to read discharge when it was really charging. Watch the needle and turn on the headlights withe the engine and key off. See if it deflects and which way. It should go to D slightly.
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Old 07-12-2013, 09:30 PM   #8
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Re: Ammeter not working

I did not cross the wires, I replaced them one at a time. The needle was that way when I put the cluster back in, but it did not move at all. After I replaced the fuses it moves now but goes to the discharge side at rest. I will e changing the cab in the future and have another under dash harness I will be using. This harness has been hacked before so it is probably in the harness.
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Old 07-12-2013, 09:44 PM   #9
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Re: Ammeter not working

The battery gauge inputs are ~12V and ~12V, but at different points in the wiring harness. So the gauge reads the difference in voltage between those two points in the harness.

WTF does that mean!?

When the alternator is working, it's making more than 12V. So close to the battery (12.6V) the voltage will be lower than close to the alternator. The gauge reads C.

When the alternator is not charging, the voltage closer to the battery with a load will be higher, and that gauge will read D.

You can measure the voltage to ground at each battery gauge terminal and subtract one from the other to get the difference. Don't put 12V across the terminals of the gauge as it's meant to move the needle via 1-2V, not 12V. Chances are 12V will just peg the needle one way or the other, but...

So, if the needle points to D when the system is working (charging) (you checked, right?), somehow, the voltage is higher closer to the battery.
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Old 07-13-2013, 10:37 AM   #10
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Re: Ammeter not working

....................................

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Originally Posted by franken View Post
The battery gauge inputs are ~12V and ~12V, but at different points in the wiring harness. So the gauge reads the difference in voltage between those two points in the harness.

WTF does that mean!?


What it means is that the gauge reads the voltage differential between the battery state of charge and the alternator output.If the alternator is working as it shoud then the gauge will read "C" and if the battery voltage is higher than alternator output then the gauge will read "D"'.

In order to do this the ammeter needs a path between the battery and the alternator for the two points to connect to. This path is called a shunt and the ammeter is connected across it in parallel. The ammeter only measures a small percentage of the voltage in the shunt as the total amperage going through the shunt would burn up the ammeter. This is the reason for the two small 4 amp fuses in the ammeter wires. The older cars and trucks used a meter that had all the power in the circuit running through it, but it measured the amps in the circuit and it was called an "Amp Meter". As more circuits were added over the years it became impractical and even dangerous, so the factories went to the battery gauge or as we call it the ammeter. It has nothing to do with amperage and instead measures "differential voltage" between the battery and the alternator. It also does not tell us anything about the circuit, except whether the alternator is charging or not.

Here is a diagram describing the shunt and the ammeter fuses and it shoes the connection points for the ammeter.


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The fuses are circled and the arrow points to the shunt. When one of our members installs a one-wire alternator or rewires the circuit he sometimes moves the output connection of the alternator directly to the battery, and off the end of the shunt and then the ammeter stops working.

The best solution is to connect the more modern "voltmeter" that only has to be connected between the positive and negative sides of the circuits.




When the alternator is working, it's making more than 12V. So close to the battery (12.6V) the voltage will be lower than close to the alternator. The gauge reads C. TRUE

When the alternator is not charging, the voltage closer to the battery with a load will be higher, and that gauge will read D. TRUE



You can measure the voltage to ground at each battery gauge terminal and subtract one from the other to get the difference. Don't put 12V across the terminals of the gauge as it's meant to move the needle via 1-2V, not 12V. Chances are 12V will just peg the needle one way or the other, but...YES MORE OR LESS


A good example of this would be substituting an air compressor for the alternator and a pressure tank for the battery. If you put a pressure line between them (shunt) and connected a pressure gauge from each end of the line, when the pressure was above kick in it would show compressor pressure
or "charge" and if the compressor pressure dropped below kick in it would show air tank pressure or "discharge"



So, if the needle points to D when the system is working (charging) (you checked, right?), somehow, the voltage is higher closer to the battery.
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Old 08-09-2013, 04:29 PM   #11
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Re: Ammeter not working

Vettevet thanks for the diagram! One fuse was good and the other was blown. I replaced it and nothing happened. I'll start trouble shooting in a couple of weeks.
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Old 08-09-2015, 05:29 PM   #12
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Re: Ammeter not working

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I did a search and came up with this post. I too have not had a working ammeter the 3+yrs. I've owned my '67. I knew it didn't work and used the dead battery as my meter LOL.Replaced alt.& ext.regulator. My question is where are the fuses. It has been told they're behind the rad support. I can't find them there on the '67. Also the wire schematic vetvet supplied is great but my junction block on the passenger fender only has 2 wires.The battery/charge voltage is low sitting high running the alt.is charging. So where are the fuses,anyone have a photo for this confused dude.I am not an electrician!!!!
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Old 08-09-2015, 05:34 PM   #13
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Re: Ammeter not working

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This is the junction block on the ol'e 67 2 wires
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Old 08-09-2015, 07:53 PM   #14
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Re: Ammeter not working

Quote:
Originally Posted by Redline novdog View Post
Attachment 1434248

Attachment 1434249
I did a search and came up with this post. I too have not had a working ammeter the 3+yrs. I've owned my '67. I knew it didn't work and used the dead battery as my meter LOL.Replaced alt.& ext.regulator. My question is where are the fuses. It has been told they're behind the rad support. I can't find them there on the '67. Also the wire schematic vetvet supplied is great but my junction block on the passenger fender only has 2 wires.The battery/charge voltage is low sitting high running the alt.is charging. So where are the fuses,anyone have a photo for this confused dude.I am not an electrician!!!!
The alternator side fuse is usually near the voltage regulator and the horn, and the battery side is usually just downstream of the junction block on the fender. See my next answer.


Quote:
Originally Posted by Redline novdog View Post
Attachment 1434250
This is the junction block on the ol'e 67 2 wires
I see your junction block has only two wires, the fusible link from the battery post and the charging wire from the alternator junction in the harness. Look at my diagram in the post above. It shows the wires and the fuses but not their actual locations.

Now here is what I'm thinking, My 67 does not have either of these wires or fuses because it came from the factory with the charging light dash cluster which does not have an ammeter or the wiring or fuses. I believe someone ahead of you may have slapped in a battery gauge dash and didn't know how to convert to it so they didn't add the wires or fuses.

You should be able to see the two small wires going to the firewall block or at the cluster plug on pins 1 and 12. If they are not in the harness you'll have to add them and the fuses. I also see a lot if corrosion on the fender junction bolt that you need to clean up, but you can do that later.
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Old 08-10-2015, 06:23 AM   #15
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Re: Ammeter not working

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No way of knowing what the PO had done,but the truck/dash should have gauges.Thank you for clarifying Vettevet.Your knowledge of these electrical systems is very helpful. Yes I need to cleanup the junction block LOL!!
I'll hopefully look at it after work,off to start another work week!!!
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Old 08-11-2015, 06:22 AM   #16
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Re: Ammeter not working

After a closer inspection last night. I think I found one fuse,under the top of the left front of fender.The next site pretty much shut the work down.The harness is a chopped/spliced/taped up mess.Time to either save up for a new harness or spend the time to replace bad with good wires one at a time.
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Old 11-02-2015, 10:55 AM   #17
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Re: Ammeter not working

Update: I have replaced the underhood harness, underdash harness, and gauge cluster (rebuilt from TBONE1964), and I still have the problem. The gauge works, just in reverse. Shows discharge when it is actually charging. I know the charging system is working, I checked voltage at the battery and the alternator to confirm this. Any other suggestions?
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Old 11-02-2015, 04:55 PM   #18
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Re: Ammeter not working

I am not an electrician by any means. but what Vettevet stated early on in the thread should help. Battery low? is there more resistance on one side than the other. Is the guage hooked up correctly? I'm just asking to bump! Good luck!
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Old 11-02-2015, 06:12 PM   #19
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Re: Ammeter not working

Recheck your connections on the cluster plug. I think you my have no. 1 and no.12 reversed. What does the meter read when you turn on the lights with the engine off?
If it reads toward C then it's probably wired backwards.
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Old 11-02-2015, 06:31 PM   #20
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Re: Ammeter not working

When I turn the lights on with the key off, it goes toward D. How would the terminals 1 and 12 get reversed? The only thing I disconnected was the plug from the cluster. Can the plug go in two different ways? I thought it was made to only fit one way.
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Old 11-02-2015, 07:50 PM   #21
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Re: Ammeter not working

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Originally Posted by 70STOVEBOLT View Post
Update: I have replaced the underhood harness, underdash harness, and gauge cluster (rebuilt from TBONE1964), and I still have the problem. The gauge works, just in reverse. Shows discharge when it is actually charging. I know the charging system is working, I checked voltage at the battery and the alternator to confirm this. Any other suggestions?
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When I turn the lights on with the key off, it goes toward D. How would the terminals 1 and 12 get reversed? The only thing I disconnected was the plug from the cluster. Can the plug go in two different ways? I thought it was made to only fit one way.
Well, that seems to rule out the meter being wired backwards. As VetteVet said, being backwards would cause it to read toward C with the key off and lights on.

Terminals 1 & 12 being reversed is something that could accidentally happen when re-pinning a warning light harness to work with gauges. But with new harnesses they should be wired correctly. And the cluster plug only fits one way ... forcing it in the wrong way would cause problems with more than just the ammeter.

The ammeter showing discharge (D) both with & without the engine running seems to indicate a problem with the charging system. I know you said you checked the voltage at the battery & alternator, but I'm thinking it might be a good idea to double check and make sure the battery is indeed charging.
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Old 11-03-2015, 09:23 AM   #22
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Re: Ammeter not working

Checked it again last night. At the alternator, with the engine idling, it is putting out 13.56 volts. At the battery with the engine idling it is 13.5 volts.
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Old 11-03-2015, 12:44 PM   #23
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Re: Ammeter not working

Just to clarify what this gauge really is, its a milliamp meter not a volt or amp gauge. It measures the amperage flow difference between two points in the system. On the 67-72 is between the battery sensing wire connection and the battery. as stated there is a small fuse on each lead.
If the Amps flowing from the alternator are greater than the amp flowing from the battery is reads +. if amps are greater moving from the battery to the alt sensing wire it reads -. The sensing wire is also connected to the systems power feed.
A few things I have come across are

The wires are backwards.
Fuses blown
The dash light for the gen light is in the socket and working, remove it if you have a gauge
Corroded connection at the sensing wire solder or at the battery connection.
Corroded or burned terminals in the cab pass though block.
A resistor in the alt wire is bad or the wrong resistance.
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Old 11-03-2015, 01:01 PM   #24
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Re: Ammeter not working

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At the alternator, with the engine idling, it is putting out 13.56 volts. At the battery with the engine idling it is 13.5 volts.
Have you tested it at higher engine speeds? And if so, does the voltage go any higher?

A "12 volt" lead-acid battery won't start to charge until the voltage gets up into the 13.6 to 13.8 V range. Even then the charging rate will be rather low and probably won't register very high on the stock battery gauge. For a safe and reasonable rate of charge you'll want to see the alternator output in the 14.2 to 14.5 V range.

Your 13.56 / 13.5 V readings might simply be due to the fact that they were measured at idle speed. It's not uncommon for the alternator output to drop off at low rpm's. Try revving the engine up a little and see if the voltage increases.
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Old 11-03-2015, 04:26 PM   #25
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Re: Ammeter not working

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Have you tested it at higher engine speeds? And if so, does the voltage go any higher?

A "12 volt" lead-acid battery won't start to charge until the voltage gets up into the 13.6 to 13.8 V range. Even then the charging rate will be rather low and probably won't register very high on the stock battery gauge. For a safe and reasonable rate of charge you'll want to see the alternator output in the 14.2 to 14.5 V range.

Your 13.56 / 13.5 V readings might simply be due to the fact that they were measured at idle speed. It's not uncommon for the alternator output to drop off at low rpm's. Try revving the engine up a little and see if the voltage increases.
Minimum voltage required to charge a lead-acid battery is 2.15 volts per cell. That equates to 12.9 volts required to start charging a standard car battery. If ANY of the 6 cells are not being charged at the minimum 2.15 volts, NONE of the cells will charge. A charge, is a charge, is a charge, no matter if it's little, or big. It is generally accepted however, to charge a vehicle battery at a higher rate, because it induces the charge more quickly.

In your case, the difference between the charging rate and the battery voltage isn't much, so you shouldn't expect to see hardly anything on your gauge.

A properly set up charging system with a functioning gauge really doesn't register much in regards to needle movement because the source voltage (battery) and alternator output should be as little as possible to maintain the battery charge. Of course, added electrical components can change the demands.

This is the reason I use a voltage gauge behind the stock amp faceplate. My amp gauge never visually indicated anything to me at a glance.

Just because your gauge used to work properly, doesn't mean it works now. It could have been on it's way out before and the changes you made pushed it over the edge.
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