Erratic Ammeter

67Dart273 said
There are several things this could be. Those here who know me know that I "HATE" throwing money/ parts at a problem. But in this case I'd try a new voltage regulator pretty quickly

Some other ideas:

1....READ the MAD article. Even if you don't do the mod, this presents an overview of "what is wrong" with many of these girls

Catalog

2....Perform my (posted many times LOL) voltage drop test. You can have drop both in the ground circuit AND the ignition / supply circuit

A.....Ignition drop: With engine stopped, key in "run" position, hook multimeter to VR "ign" terminal, hook other terminal to battery POS terminal. You are expecting a very low reading, the lower the better. Anything over .3V (3/10 of one volt) go looking for trouble

B....Ground. Run this test with engine running fast, battery "normalized" and first with accessories off, and again with lights heater, etc on

Stab one probe into the mounting flange of the VR. Stab the other into the top of the battery NEG post. Again, you are hoping for a very low reading, zero is perfect

3....VR MUST be grounded. Remove, scrape around bolt holes on firewall and back of VR and remount using star lock washers

4...General causes of drop. Again, the MAD article is a source, the diagram they have there is a good simplified view of the main power distro:

Drop generally occurs at ANY terminal, but there is usually about THREE or FOUR points "in" any "one" terminal!!! Take, EG, one terminal in the bulkhead connector: You have the (1) wire crimp on the firewall terminal......(2) the terminals "connection" itself, and (3) the wire crimp on the passenger compartment side. THAT ONE TERMINAL then has actually 3 points for "drop." That wire (big red) goes to the ammeter, you have about 4 fail points right there, the wire end terminals, the ammeter stud connections, etc etc, and out the BLACK ammeter wire to the WELDED SPLICE. "Tuck that" away for last, because rarely, they DO fail!!!! Next onward to your ignition switch.......You have (1) the crimp at the switch connector terminal feeding the switch, (2) the termination between the connector and switch, (3) the contacts in the switch (which may count as TWO) and (4) the IGN1 terminal at the switch, (5) the connection between it and the connector, and (6) the crimp on the the ignition wire (dark blue IGN1) coming out of the switch, and then THREE more going back out through the bulkhead connector!!!!!

The "point" is you have all these series points where failure(s)...(s) can occur and add up.

THE VOLTAGE YOU MEASURE in the voltage drop test is ADDED to a properly working VR, AKA if you show 2v drop, and the VR is properly working at 14, then your battery will "see" 17V!!