ammeter fuses

[Papa Smurf]

Can someone help me locate or identify the fuses in the ammeter circuit.

I have a 72 GMC with 4-amp inline fuse holders, one by the battery and one by the driver's side headlight. When these are blown the gauge doesn't work.

On my 72 swb chevy I can't find these fuses and my gauge doesn't work.

The alternator is working because I can unhook the battery with the truck running and it doesn't die.

[RustyPile]

Let me begin with this... Never, never disconnect the battery while the engine is running.. Voltage spikes develop that will take out the diodes, and other parts in the alternator..

Consult a wiring diagram. If the fuse and fuse holders are missing, of course the gauge won't work.. The ammeter circuit is basically a shunt and isn't required for the charging system to function properly. The wiring for the gauge is totally independent of the other wiring. One of the wires is black and the other is black with a white tracer. If they are still in place, both holders are very visible, try to locate them. If the charging system has been upgraded with larger gauge wiring and an internally regulated alternator, the ammeter readings will be totally inaccurate.

[Accelo]

Interesting, as you have found the fuses in the only place I KNOW them to be.
Just remember this is a shunt and both sides are +12V.
I would begin by checking for voltage on both gauge terminals.
You must disconnect one of the terminals to confirm you are not reading voltage through the gauge.
It says Volts on the gauge, but it is reading milliamps.

[franken]

The stock gauge is marked C and D for charge and discharge.
It reads the difference between the voltage near the battery and near the alternator. There are no milliamps involved.