I could not find anything useful about testing whether my ammeter works or doesn't but I don't think I checked the archives, so if it's there let me know.
My needle does not seem to ever flinch off dead straight up. No +, no -.
Per the wiring diagram there are two wires to/from the ammeter, a BLK and a BLK/White. Both ultimately go to the positive side of the battery so I'm confused.
I was a mechanical engineer but drank my way through the electrical portion of my college degree. Sorry. BLK/White wire goes to the horn relay positive, BLK wire to the
starter solenoid positive side.
When I put my multimeter on the BLK wire to ground with the engine running I get 12-13 V. When I put it on the BLK/White wire to ground I get 0 V.
No I do not have a spare ammeter lying around to hook up and my test tells me nothing about whether my ammeter works. Can somebody please
tell me what this means. Thanks, Craig

 

See if this helps, not sure if there is a difference between C2 and C3 ammeter
http://repairs.willcoxcorvette.com/1...ing-amp-gauge/

 

A C2 doesn't have a true ammeter. It has a battery gauge. It has a red wire that ties from the starter positive to the horn relay, then a black wire to the starter end and a black/white wire to the horn relay end. The battery gauge reads the voltage drop on the red wire and deflects in the direction of the drop. More current, more voltage, thus more movement of the needle. It is marked +40 and -40 but trust me 40 amps does not flow through that gauge. That is just an indication of more current flowing through the red wire mentioned, which is measured by the gauge as a small voltage because the total resistance of the wire is less than one ohm.
If you want to test the needle deflection, connect a small 1.5v battery with a jumper to the black and the black/white wire on the back of the gauge MOMENTARILY and the needle will deflect in the direction of current flow, either positive or negative. I takes a very small voltage to cause full scale deflection in the gauge, so don't leave it connected, just touch it.
If your battery is fully charged, there will be very little movement off zero except momentary deflection when you turn on headlights or roll them over, or step on brake. Just for your information and testing assistance remember this. The gauge is active and reads ALL the time, key off or on, AND both the black and the black/white wire on the gauge will have 12v battery voltage on them at ALL times, key off or on. So don't touch either wire to ground anywhere. You will melt the wires or blow the gauge.

 

Here’s your test. With key in the ON position and the engine NOT running. Turn on your headlights and put them on high beam, then turn on your heater fan to HIGH. Blow your horn. Your battery gauge should show a serious negative deflection.

Leave the lights and blower on for 30 to 60 seconds then turn off the lights and blower and start the car. You should see the gauge deflect to the positive for a brief period until the charging system stablizes.

 

Craig, this symptom is indicative of the problem with your meter, which in all probability is good.

As counter intuitive as it seems, there should be Voltage on both terminals of the Ammeter at all times. The fact that one terminal is showing 0 Volts says that there is a discontinuity in the wire to that terminal. It could be a break in the wire or it could be a poor connection at the firewall connector on the driver's side.

Find and fix that discontinuity and I bet your Ammeter will work.

Jim

 

Remember that the black AND the black/white wires pass through the bulkhead connector closest to the centerline of the car. You could have a bad connection in that connector; Read the voltage on your black wire at the starter 12v lug. You may have a bad connection on the ring to wire connection there, or it could be broken in between. Or the wire may have pulled out of the ring connector. As mentioned, both the black and the black/white wire should read battery voltage at all times the battery is connected.

 

Thanks to all for the feedback. I did a continuity check across the gage terminals and got positive results, gage good. I did the overload the battery test with lights on, blower on, etc. and saw a movement to the negative side. I checked the continuity of both wires from the gage to their termination and got good results. It seems as though the gage is working fine, I was just assuming that whenever I goosed the gas or ran the RPM's up I would see more of a movement to the positive side as the alternator put out more volts. Good to know it works.
Thanks Again for the education and tips, Craig

 

Jim, thanks. I'm not really sure why I did not see voltage on the BLK/White wire when I grounded it. Maybe user error. I may re-check. The wire DID have continuity from the horn relay terminal to the connector on the gage. Craig

 

No. One of the chief advantages of the alternator over the generator is its ability to provide stable voltage at low RPMs....
On a properly operating C2 you shouldn't see the alternator go much positive, nor your lights brighten appreciably, when blipping the throttle from an idle...

Here is my alternator charging at very close to an idle:

 

Yep, that's strange all right. Since your gauge otherwise seems to work, I suspect the probe of your DVM just didn't make good contact with the meter terminal.

Congrats on getting it resolved.

Jim