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.

[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