Change out that main wire and the alternator either quits working or it loses its calibration. But, when installing a higher capacity alternator and other high current components, that wire NEEDS to be enlarged to be safe. You could add another 'parallel' wire to gain capacity, the ammeter calibration will be 'off', but it will still function, as long as the original harness is left intact.

 

Just to clarify- this car has had a crate 383 and new alternator put in 15 years ago.. im only guessing they made all necessary wire changes at that time. Although perhaps if they didn't. Could that explain the failed ammeter?

I'm tempted to repair the ammeter and just see if it works before I go tearing into my wiring.

 

If you measure voltage on the two wires that go to the ammeter and they both measure 12 vdc, your ammeter may work just fine. The voltages are slightly different (millivolts), but that difference is not easily measured on a common VOM. If you hook it up and it works, pull on the headlamps and see which way the ammeter needle swings. If to (-) discharge side, all is good, If it swings to the (+) charge side, reverse the two leads and NOW all is good. If you get no swing, the original wiring may be "revised" and conversion to a voltmeter may be the best choice.

 

Agreed. quite possible some revisions have been made. Unfortunately the previous owner really only cared about horsepower and didn't give a lot of thought to keeping up with the electrical systems of the car. I'll update thread when I can get around to fixing the gauge. Do voltmeters designed for replacing (directly) these ammeters exist? Or does one have to modify a different gauge. It would seem to me that finding some switched DC and landing the other side of the gauge to ground would be pretty easy.

 

C3's went to voltmeters in 1977. The dial face is a bit different; but it will fit in the same gauge console hole. I would think that you could use EITHER of the original ammeter leads (as long as it still has 12vdc when the ignition is in AUX or RUN position) for the positive connection, and connect the negative post on the meter to chassis ground (metal in the dash area).

 

Well I decided to dive into this tonight to resolve it once and for all.

Taking the center console apart to access the ammeter was actually pretty easy.

Upon testing the ammeter I found that it appeared the coil was open.

I took the ammeter apart and discovered no broken wire! As I inspected the gauge I realized that this was probably not the factory gauge, as you can see in the picture, there insulated coating on the coil winding was never removed when it was soldered to the post!

A) They likely replaced the gauge and gave up when it didn't work

B) what seems very unlikely- it never worked from the factory.

C) they attempted a repair and botched the job.





Some quick sanding and solder work got everything back in order. Gauge tested well and problem is solved! (Picture is before repair was made)

I made no changes to my wiring harness.

I just threw it in, turned on some load and saw the meter deflect towards the negetive direction. Turned the engine on and it deflected right, and gradually came down to settle on the 0.

Hopefully it works well for a long time. Thanks to all for the advice!