1972 C10 Ammeter question

[wlt3355]

I was diagnosing why my fuel gauge quit working and removed the instrument cluster to check it as well, and discovered the circuit board had three lines shorted out.

Both lines going to the ammeter were shorted out as well as one line coming from a grounding spot.

I discovered on the back of the ammeter that there is not any insulating material between the back of the stud nuts and the metal panel board, which in my mind, allows for a direct short between the battery terminal, the alternator terminal, and the ground within this panel board. (see attached pictures)

Am I correct on this that there should be some type of an insulating material between the stud nuts and the board, as there is on the back side, just not the inside.

Also could this have been the problem with the fuel gauge quitting?

[LockDoc]

Originally Posted by wlt3355

I was diagnosing why my fuel gauge quit working and removed the instrument cluster to check it as well, and discovered the circuit board had three lines shorted out.

Both lines going to the ammeter were shorted out as well as one line coming from a grounding spot.

I discovered on the back of the ammeter that there is not any insulating material between the back of the stud nuts and the metal panel board, which in my mind, allows for a direct short between the battery terminal, the alternator terminal, and the ground within this panel board. (see attached pictures)

Am I correct on this that there should be some type of an insulating material between the stud nuts and the board, as there is on the back side, just not the inside.

Also could this have been the problem with the fuel gauge quitting?

The insulators are built into the back of the gauge. If you look closely you should see a small white plastic ring around the base of each mounting stud. If these were not centered in the holes when the gauge was installed they would short out for sure.... If that gauge was installed the way it is now it would be wrong. The rectangular insulator and nuts shown should be on the outside of the mounting plate. And yes that would be a direct short.

LockDoc

[dmjlambert]

It does seem to me that there would be some sort of insulator on the ammeter posts, and that scorch mark on the printed circuit looks bad. I don't know what the insulator pieces look like, but perhaps somebody with an extra good condition instrument cluster will chime in. (Edit: I see LockDoc already chimed in about that while I was writing my long-winded post)

At first I was going to say it does not seem like that could be related to a problem with the fuel gauge, because the fuel gauge is pretty far from that area. But then when I look at the printed circuit diagram, the part of the printed circuit with the scorch mark does connect to one side of the fuel gauge. One of the traces that goes to the temp gauge also goes to the fuel gauge. If you had a short that melted the plastic in the area that carries those 4 copper traces, it could cause shorts.

Those 2 places where the ground screws connect to the metal of the instrument panel are intentional. That is how ground on the printed circuit gets connected between the screw near the main connector and the screw near the high-beam indicator.

If you want to continue troubleshooting your fuel gauge and use the instrument cluster without the ammeter hooked up, you should be able to remove the fuses that go to it if they are not already blown. Based on the scorch marks I would be surprised if they are not blown because they are only 4A fuses. They are in rubber capsules, one near the driver side headlight and one near the battery junction block on the passenger side fender.

Here is a thread with a diagram of the printed circuit.
http://67-72chevytrucks.com/vboard/s...d.php?t=709847

[wlt3355]

Thank you gentlemen, as far as any insulting plastic rings, this one does not have any on them, but I could create a couple easy enough to shield the studs from the metal. So with that being said, then I would also assume that the two metal nuts should not be touching the board as well without an insulator in between them?
On the outside of the board, there was an insulator, but not on the inside.
Thanks again

[wlt3355]

And there they are "the plastic rings I was missing"

[wlt3355]

Thanks again for your help. I removed that insulator and found those two plastic rings, and realized that the brown insulator board was installed incorrectly (I think) with those two nuts touching the panel board, the nuts should go on the outside of the outside insulator, thus creating this barrier.

I also found my two 4 amp fuses, and yes, they were blown.

[LockDoc]

Originally Posted by wlt3355

And there they are "the plastic rings I was missing"

Yep, that's them. They just fit inside the holes in the mounting plate then the rectangular insulator and nuts go on the outside....

LockDoc

[dmjlambert]

So, the only thing wrong was the order of assembly?
You may need a new printed circuit if some of the traces are fried and the plastic they rest on is melted. Otherwise you would have to get creative with a repair to the printed circuit and that is somewhat difficult work. I have not needed a new printed circuit yet, but I noticed that Manes Truck Parts sells used ones.

[LockDoc]

-
I have soldered a small jumper wire across damaged traces for testing purposes but I would replace it for the long haul....

LockDoc

[Boog]

Don't take any chances with it. Questionable electrical connections can and do lead to fires. If it looks bad replace it. No place to skimp on repairs.

[wlt3355]

Thanks guys for all of your help today. I did discover this was hooked up incorrectly. I also had ordered a new circuit board already so can install this tomorrow feeling better that I will probably not short this one !

[LockDoc]

Originally Posted by wlt3355

Thanks guys for all of your help today. I did discover this was hooked up incorrectly. I also had ordered a new circuit board already so can install this tomorrow feeling better that I will probably not short this one !

No problem, that's what we like to do on this board. Let us know the outcome on your replacement....

LockDoc

[wlt3355]

Good news. after new circuit board and installing the ammeter in the correct position, it works great!

Bad news, now temperature gauge is not working and fuel gauge still does not work, actually sitting around 8:00

But ammeter works.

[dmjlambert]

Regarding the temperature gauge, you can take loose the connector from the temperature sensor on the engine, and short it to ground with a piece of wire or alligator clip test lead. See if that pegs your temperature gauge.

Same thing with the fuel gauge, take loose the connector from the fuel tank sending unit, and short it to ground and see if that pegs your fuel gauge. It should read above full when the wire is disconnected, and below empty when the wire is shorted to ground.

I have a rebuilt engine and the heads are from a 90s crate motor, so the original and correct temperature sender does not fit in my engine. When my engine is hot, it barely reads anything on the temp gauge. There are threads on the forum that talk about what to do about that, but I haven't done any corrective measures yet to get my temp gauge going.

[LockDoc]

Originally Posted by dmjlambert

Regarding the temperature gauge, you can take loose the connector from the temperature sensor on the engine, and short it to ground with a piece of wire or alligator clip test lead. See if that pegs your temperature gauge.

Same thing with the fuel gauge, take loose the connector from the fuel tank sending unit, and short it to ground and see if that pegs your fuel gauge. It should read above full when the wire is disconnected, and below empty when the wire is shorted to ground.

I have a rebuilt engine and the heads are from a 90s crate motor, so the original and correct temperature sender does not fit in my engine. When my engine is hot, it barely reads anything on the temp gauge. There are threads on the forum that talk about what to do about that, but I haven't done any corrective measures yet to get my temp gauge going.

On the fuel gauge you can also ground it at the "fuel" terminal on the fuse block if you have trouble moving the seat far enough ahead for access to the wire.

Here is one of the better threads on the temp sender conversion for Vortec and LSx heads.

http://67-72chevytrucks.com/vboard/s...d.php?t=703388

LockDoc

[wlt3355]

Thanks will check both of them, the sender unit is new and was working great before I replaced this board, it appears that there is not any power coming from the pink wire in the cluster. This appears to feed one leg of the fuel gauge, two lights, and one side of the temperature gauge, so I think my problem is here. I am not sure where that power comes from for this terminal.

I do have that very difficult seat that will not fold, or actually even move much, may have to remove it to see.

It appears the fuel terminal at the fuse box is a ground terminal, is that correct?

[LockDoc]

Originally Posted by wlt3355

Thanks will check both of them, the sender unit is new and was working great before I replaced this board, it appears that there is not any power coming from the pink wire in the cluster. This appears to feed one leg of the fuel gauge, two lights, and one side of the temperature gauge, so I think my problem is here. I am not sure where that power comes from for this terminal.

I do have that very difficult seat that will not fold, or actually even move much, may have to remove it to see.

It appears the fuel terminal at the fuse box is a ground terminal, is that correct?

Power for the pink wire comes from the fuse block/ignition switch. Check all of the fuses close and check for rust in the fuse holders.

Basically yes, it is a ground terminal.

Here is a thread for the wiring diagrams. If you scroll down below the pictures on the first two posts there is a link to larger versions.

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

Here is the best thread on fuel gauge diagnostics.

http://67-72chevytrucks.com/vboard/s...d.php?t=640615

LockDoc

[wlt3355]

ok, update,

Found a bad fuse in box, replaced, got power back to temperature, which now works, good...

fuel gauge still not working, removed seat, removed sender wire, turned key on, fuel gauge goes to full.

So does this probably mean a float issue?

[dmjlambert]

I'm thinking yes, if you have a full tank of gas. I have heard of people replacing the floats, but I just got a whole sender unit because I wanted to have fresh pipe, and sock, and variable resistor. If I were you I would just pull out the whole sending unit, and use a jumper cable to ground it, and hook it up to the sending wire and move the float up and down and see how the gauge acts, and check the condition of the float and sock. I remember it being fairly easy to remove and replace the sender, I just used a big pair of pliers with the jaws open to press against and turn the little wings that loosen/tighten the unit, it was something like a quarter turn to take it off.

[wlt3355]

Found my problem, float had a tiny hole in it and was full of gas...need to get another float

[LockDoc]

Originally Posted by wlt3355

Found my problem, float had a tiny hole in it and was full of gas...need to get another float

Any vendor should be able to help you with that. Postage will be more than the part...

LockDoc

[wlt3355]

Just ordered the whole sender unit,

and thanks again to everyone for your help...pretty well got everything working now

Walter

[LockDoc]

Originally Posted by wlt3355

Just ordered the whole sender unit,

and thanks again to everyone for your help...pretty well got everything working now

Walter

Good deal. Let us know if you have any other questions....

LockDoc

[LongBox]

I see you have already ordered a new sender unit, but repairing the float is a piece of cake. I simply removed the gas from the float, sanded the area near the crack, fluxed it, and soldered it using a large electric soldering iron. Might be good to keep the old unit as a spare, or cancel the order for the new one.

[LockDoc]

Originally Posted by LongBox

I see you have already ordered a new sender unit, but repairing the float is a piece of cake. I simply removed the gas from the float, sanded the area near the crack, fluxed it, and soldered it using a large electric soldering iron. Might be good to keep the old unit as a spare, or cancel the order for the new one.

Worth a try but when I tried soldering one the pressure from the iron heating up the air inside the float kept blowing the solder out of the hole....... I know, I know, you have to be smarter than the float to get it done...

LockDoc