Hi,

I have a 1972 F250. The ammeter in the dash is not working. I removed the dash and tested meter. The meter works. I believe the problem is in the wiring. I cleaned the terminal connection at the back of the instrument cluster, but no difference. I don't have a wiring diagram for this year. Could someone post a diagram?

I do own and use a multimeter.

Any help is appreciated,

zenmaster

 

The original ammeters never really worked that well in the first place. If someone has replaced the wiring for the alternator, more than likely they did not re-use the shunt in the harness for the ammeter to work.

I don't have a diagram for your truck, but if you can find out what the color wires are that go to the ammeter, then go out and find the large output wire on the back of the alternator, and follow it all the way to the splice and then to the large terminal on the solenoid. Somewhere along the way you should come to a strange place in the wire, and the two small colored wires from the ammeter should be soldered across this piece in the alt wire.

This piece in the wire is called a shunt. It's a very small measured resistance, and creates a voltage drop across, depending on how much current is flowing through it. The ammeter in the dash is really a very sensitive voltmeter, and it's reading the small voltage created by the shunt.

 

Thanks Franklin2,

I'll have a look on the weekend and see if I can locate the problem.

zenmaster