I retrofitted my 69 Camaro with factory console gauges about 10 years ago. The amp meter never moves more than the width of the needle in either direction but does respond as you'd expect when lights are cut on etc. After rechecking my wiring, everything appears correct.
Can someone tell me the resistance the gauge should measure across the black and black/white terminals? I don't believe this gauge uses a ground, but please let me know if I am mistaken.
Neither terminal on my gauge shows a connection to ground and the resistance between them is 0.6 ohms. When running, I have about O.150v between the horn relay splice in the harness and junction block when drawing 15A from the battery (high beams, dome light etc.). At the gauge I only see 0.015V during these same conditions.
I don have a EE degree but it's been 10 years since I cracked a book, so tell me if I'm being an idiot :)
My 1964 vette does the same thing.
The new / transistorized voltage regulators show hardly any movement (for information's sake).
I'm wondering if the under hood wiring harness for gauge cars might have used a different wire between the junction block and horn relay. With the key off and a 15-18A load, I see a 0.1V drop between the two points.
I know these gauges are sensitive, but I expected more of a voltage drop. I hear they are a 0-1V range. 15 amps is at least 1/3 of the scale and should be closer to 0.3V.
My amp gauge in the console on my 68 barely moves as well. So, fingers crossed when I take the car out. The only other console guage I have hooked up is the fuel guage,...my oil pressure and temp are aftermarket guages,
I got this information from Mark C on camaros.net (and CRG) when I smoked my original ammeter. I had made a sub-panel for a USB charging point. That's all it took.
"There is no ground needed on the stock console "ammeter". It is really a -0.5 to +0.5 range millivoltmeter labeled in Amps. It uses the resistance of the red charging wire that runs between the horn relay and the battery to provide the voltage drop to deflect the needle. When the battery voltage is higher than the horn relay terminal voltage the needle deflects down scale towards discharge, when the horn relay volatge is higher than the battery voltage, the needle deflects upscale towards charge. That's all there is to it.
If you tried to run any kind of current thru it, like grounding either end of the black, or black with white trace wire, while the other is still connected, you ran 12V thru a 1V range meter and probably smoked it.
It doens't take alot of current to burn up the wiring in the gauge itself. If you've replaced the red wire that runs across the radiator support from the horn relay to the battery terminal with a large size wire the gauge may not even register the difference and will sit at the 0 point all the time because the voltage difference across that wire for normal charge or discharge currents is no longer high enough. Do not under any circumstances try to run current thru the gauge, or attach anything to the circuit higher than 1V DC, you will be buying a new gauge if you do that.
Measure battery voltages at the console connector on the black and black/w wires. You should see battery voltage on both, if not the wires are open somewhere."
Learn something new everyday.I also ways wondered how the guage handled current flowing through it. Now I understand that it does not flow at all.
As Hawk suggests, the GM OE designed ammeter is actually a millivolt meter and indicates the voltage drop between the horn relay buss bar and battery junction block of the red wire installed.
One would need an aftermarket ammeter and #8 AWG wire and install ammeter between the disconnected red OE wire and the relay buss bar.
I discovered my problem.... Years ago I soldered the crimp connection at the horn relay splice where the wires In the harness split to run back to the gauge. Soldering this connection lowered the resistance enough to effect the gauge. The lower the resistance of the connection the lower the voltage drop and effecting the sensitivity.
To fix the problem I added a length of wire between the in harness splice and the junction block. The gauge now reads accurate.