Amp Gauge

[tdangle]

Weird problem, with the engine off if you turn on the headlights the amp meter swings toward the C side. With the engine running and charging the battery it swings toward the D side. Was my dad's truck (he bought it new) and nothing has been rewired. I've traced the wiring out and it all looks correct.

[demian5]

My 70 does the same thing.

[tdangle]

Now that's just too weird. I bet your truck was made in Fremont also. Wonder if they got a bad batch of amp meters?

[garyd1961]

It's not going to read correctly with the engine off, it's an amp gauge not a volt meter. It reads the difference between alternator amperage and battery amperage.

[RustyPile]

Amperage is defined as the flow of electrons.. If the electron flow is greater coming from the battery, the amp gauge will register a "D" or discharge.. If the flow is greater coming from the alternator, the gauge will register a "C" or charge.. The only difference in the amp gauge indication between engine running and engine off is any electron flow during "engine off" will always be "D".. Drivers misunderstanding an amp gauge function and meaning of the readings, led to many manufacturers switching to a volt meter, which is more easily understood..

The OP's faulty readings are caused by the amp gauge's wires being wired in reverse..

[garyd1961]

Originally Posted by RustyPile

Amperage is defined as the flow of electrons.. If the electron flow is greater coming from the battery, the amp gauge will register a "D" or discharge.. If the flow is greater coming from the alternator, the gauge will register a "C" or charge.. The only difference in the amp gauge indication between engine running and engine off is any electron flow during "engine off" will always be "D".. Drivers misunderstanding an amp gauge function and meaning of the readings, led to many manufacturers switching to a volt meter, which is more easily understood..

The OP's faulty readings are caused by the amp gauge's wires being wired in reverse..

Both trucks? I guess it's possible.

[RustyPile]

Originally Posted by garyd1961

Both guys? I guess it's simple physics.

There... I fixed it for you..

[Steeveedee]

I have a '70 Fremont truck, and when I turn on the lights with the ignition off, it indicates "D" like it should. Did you guys with the readings reversed check to see how the gauge reads when the engine is running?

Rusty- if physics was simple, everybody would study it!

[tdangle]

I reads reversed. drain the battery down start the truck and it swings to the d side and slowly goes to center. It is charging at aprox 14.5 volts so I know everything but the gauge is working.

[RustyPile]

Originally Posted by Steeveedee

I have a '70 Fremont truck, and when I turn on the lights with the ignition off, it indicates "D" like it should. Did you guys with the readings reversed check to see how the gauge reads when the engine is running?

Rusty- if physics was simple, everybody would study it!

Steeveedee, I heard a rumor today about you and me.. It seems you and I are the only people on this site that aren't physicists.

[Steeveedee]

Originally Posted by tdangle

I reads reversed. drain the battery down start the truck and it swings to the d side and slowly goes to center. It is charging at aprox 14.5 volts so I know everything but the gauge is working.

OK, I'm going to ask. Are you SURE the meter fuse on the battery side isn't popped? I can't tell you how many times I've looked at fuses and they looked fine but the filament had pulled off the end cap instead of the middle, like a good little fuse should do. I'm not making fun, if that thought crossed your mind. I'll tell a true story about my '69 Camaro. It had the gauge package in the console. Some of the lights were out in the gauges, so I pulled it up and put bulbs in every socket, even if it didn't have a bulb in it before. You'd think that if there was a socket, there should be a bulb in it (these pushed in). I went through a ton of diagnostics before I realized that one of those bulbs was stopping the oil pressure gauge from going above 10 or so PSI. It was a mechanical gauge, and the light bulb would not allow the Bourdon tube to move properly. Crazy.

[tdangle]

Yes both fuses are good. If either one of them is blown the meter will not read anything.

[franken]

The battery (not amp) gauge is fed by 2 voltages, one close to the battery and one close to the alternator. The gauge reads the difference in voltage. More + on the battery side means discharge.
With the engine running, I'd measure voltage to ground from each terminal. For grins, you can measure across the terminals to see the voltage difference.

[Curtb1971]

Hmmm, I wonder if the two wires are crossed at the cluster wiring connector or at the firewall bulkhead? Maybe it was a Friday at gm for building the wiring harness but with one wire black and the other black with at thin white stripe it could be easy to get messed up.

[gmc684x4]

As an industrial electrician meters do fail the amp meter could be toast too

do you have a buddy who has gauges in his truck ?

One easy test take your gauges plug into a truck known to work and test your gauges that way

[Sparky dave]

Mines a 69 Freemont truck and the gauge stays in the middle and hardly moves

[Steeveedee]

Originally Posted by tdangle

Yes both fuses are good. If either one of them is blown the meter will not read anything.

Doh! You are correct!

[RustyPile]

Originally Posted by Steeveedee

Doh! You are correct!

Go easy on the lad, Steeveedee.. With all the bogus electrical theories put forth on this thread, it's a miracle the poor guy can turn on the lights in his shop..