Help! 1974 ammeter

[Restorit]

Hi all, 1974 Ammeter doesn't seem to move at all under load,etc. Found its harness was disconnected when I pulled the guage panel off. Does anyone know if ground (Black) goes to the silver or copper terminal in the back of the ammeter? Thanks

 

[JohnZ]

Hi all, 1974 Ammeter doesn't seem to move at all under load,etc. Found its harness was disconnected when I pulled the guage panel off. Does anyone know if ground (Black) goes to the silver or copper terminal in the back of the ammeter? Thanks

The black is NOT ground. One wire (black) goes to the battery cable stud on the starter solenoid, and the other wire (black/white) goes to the alternator and horn relay - both have 12 volts on them all the time. Ground either one and you'll have a harness meltdown. Both wires should be in a plastic connector that only goes on the back of the ammeter one way.

 

[Restorit]

Ok Thanks. I mention ground because if I take an ohmmeter to the black wire and to ground it reads. The bl/wh doesn't.

 

[JohnZ]

The "ammeter" isn't an ammeter at all - it's a sensitive voltmeter (galvanometer). One lead senses the voltage at the starter solenoid, and the other lead senses the voltage at the alternator and horn relay; the gauge displays the difference in voltage between those two points, and the needle going (+) or (-) indicates whether current is flowing TO or FROM the battery. Both leads are HOT all the time with battery voltage, key on or off.

 

[Restorit]

So with the battery connected. I should see a reading if I use a voltmeter across the back of the ammeter with engine off? (or from 1 terminal to a ground if there both hot). If not, then there must be a break in the continuity of the rest of the circuit past the bulkhead somewhere?

 

[JohnZ]

So with the battery connected. I should see a reading if I use a voltmeter across the back of the ammeter with engine off? (or from 1 terminal to a ground if there both hot). If not, then there must be a break in the continuity of the rest of the circuit past the bulkhead somewhere?

You should see battery voltage on both wires, key on or off. If not, a common failure point in the circuit is bent/corroded terminals in the multiple connector on the engine compartment side of the fuse block.

 

[Restorit]

Got it, I checked and the BL/White stripe wire was originally cut and left disconnected from the junction block. Got juice from both terminals now. THX again for all the help.