Join Date: Mar 2002
Location: Austin, TX, USA
All amp guages are really millivolt meters connected across a low value resistance known as a shunt. (There are internally shunted meters, but not on Camaros to my knowledge).
The low value shunt in your car's electrical system is the wire connecting the horn relay to the juntcion block behind the battery on the radiator support. So the amp meter should be connected to both the horn relay and to the junction block.
Since the relay/B+ wire is your shunt, changing it's size will alter the meter's calibration. If you upsized the wire, as many folks do with an internal regulator conversion, the meter will read lower than normal. You may be able to compensate for the problem by changing a resistor on the back of the guage - I don't know for certain. If the guage does not have a resistor calibrator accross it's terminals you might be able to install a few ohms of resistance in series with the amp meter leads to offset it. But usually it isn't necessary. The gauge is really just a visual indicator of charge / discharge. Probably the factory setup was calibrated to no better than +/- 10% of Full Scale.
Since the meter is a millivolt meter, if you connect one terminal to B+ and the other to ground, you'll likely damage the meter movement. 12 volts is about 240 times overscale for a typical ampmeter (millivolt meter). Looks like I duped Mark C.'s point. BTW, the +/- 0.5 volt claim is probably correct. I personally haven't measured it.
To confirm the hookup, use a digital volt meter. You should be able to read just a few millivolts on the amp meter's terminals as loads are varied on the electrical system.
If you know the resitance of your shunt (by measuring it out of circuit). You can translate the voltage drop across the shunt with the current through it. Ohms law says:
I = E / R
'I' is the current through the circuit. 'E' is the voltage or eltromotive force measure accross the resistance 'R'. So if your horn relay / junction block line has a resistance of 0.1 ohm, and you measure 0.100 volts across the line, the current load is 0.1 Ohm / 0.100 volt = 1 Amp.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI