Amp Gauge ?

[70GMCer]

How would you test the Amp. Gauge to see if it is good or not? The one in my dash is not working. It is the factory one.

[Sweet72]

Only accurate way I know is to hook it up in a series circuit with a load of a known current draw. Simple test...hook it in series between a car battery and a dc motor like your heater blower motor, if the needle deflects the ammeter is probably good. Wire it like this schematic but delete R2. R1 being your blower motor, and the component on the left side of the drawing is the battery. Hope I didn't confuse you.

[JimKshortstep4x4]

The factory ammeter is wired in parallel with the main feed wire, (large red #10 wire). It gets its very, very low current input because of the resistance in the feed wire over a 3' length. The inputs for the ammeter are fused at 4 amps, (two fuses, one on each side of the radiator).

If the ammeter has continuity when tested with an ohm meter than it is probably ok. If you want to test it in series as suggested, I would make sure that the ammeter does not see over 2 amps just to be sure.

Jim

[70GMCer]

Thanks....I'll give that a try.....

[Custom/Ten]

I have a new amp meter and new printed circuit board but I'm not sure the amp meter is hooked up to the alternator, anyone know how I can check this. Wiring diagram just shows a brown wire to the generator. I'm pretty sure i have an alternator. If I were to hook up a AAA battery in place of my truck battery would that make the gauge move if its hooked up? Is this safe for my electrical system. Anyone have a better idea? I'm sure the gauge works i just don't know if all the wiring is hooked up.

[ray_mcavoy]

Originally Posted by Custom/Ten

I have a new amp meter and new printed circuit board but I'm not sure the amp meter is hooked up to the alternator, anyone know how I can check this.

As JimKshortstep4x4 pointed out, the factory ammeter is wired in parallel with the main feed wire that connects the output of the alternator to the battery. And as he said, there should be a couple of 4 amp inline fuses (one near the battery and one near the voltage regulator) where the ammeter wiring ties into the charging system. Check both of those fuses ... if either one is burned out the ammeter will not work.

Originally Posted by Custom/Ten

Wiring diagram just shows a brown wire to the generator. I'm pretty sure i have an alternator.

You were probably looking at a wiring diagram for a truck with the base equipment "warning light" instrument cluster. Those diagrams don't show the ammeter wiring.

That brown wire is the alternator "exciter" wire and isn't part of the ammeter circuit.

Even though most GM vehicles changed over to alternators in the early 60's, they continued to refer to them as generators.

Originally Posted by Custom/Ten

If I were to hook up a AAA battery in place of my truck battery would that make the gauge move if its hooked up? Is this safe for my electrical system. Anyone have a better idea? I'm sure the gauge works i just don't know if all the wiring is hooked up.

That wouldn't do any harm to your truck's electrical system. But it won't make the gauge move either.

The easiest way to see if your ammeter is hooked up and functional is to simply turn on the headlights (or other load) with the engine off. That should cause the needle to swing to the "D" or discharge side.

For additional troubleshooting, you can unplug the gauge cluster and use a test light to make sure you have power on both of the ammeter wires at the cluster connector. They'll be the black wire with the white stripe in cavity #1 and the black wire in cavity #12.

[LockDoc]

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Here is a picture of one of the fuse holders the guys are talking about. This one is by the battery. They have 5/8 inch long, 4amp fuses in them.

LockDoc

[Custom/Ten]

Thanks guys!

[Johnnyhotrod]

What would cause these fuses to blow?