66 Alternator Gauge Issue

[kingchief]

My alternator gauge jumps around while I am driving. While idling, it is ok. When I give her the get up and go the needle jumps and flutters around.

Anyone have any ideas how to resolve the issue? I have the standard 42 amp alternator and Marti voltage regulator if that helps. No other issues. Another fellow reached out to me saying he has the same issue. Thoughts???

Steve

[trotrof1]

I would probably start by checking the wiring connections at the starter relay and at the alternator. The wiring can get brittle over time.

[DennyD]

I'm having the same issue that Steve described, AMP gauge needle bounces all over when running at speed. At idle its stable. I just took your suggestion and re-checked all the connections at the starter relay and alternator. All wires at tightly connected and not brittle or worn. Any other suggestions? Should I pull the gauge cluster and check there next? Thanks

[trotrof1]

The only issue I had with my ammeter is it was dead when I bought the car and replaced it with a ford service unit. I would load test the charging system with a SUN tester or equivalent. A few of the other mustang forums traced similar issues to the regulator on the firewall.

[kingchief]

All my wires are tightly connected and are not brittle also. I will try a new regulator and see what happens...gotta find one first!!!

Thanks,

Steve

[NC TRACKRAT]

I seem to recall that a few years back, there was a mod swapping out the "guts" of our original electro-mechanical regulators with the "guts" from a new MOTORCRAFT solid state regulator.  That might help solve the ammeter problem  It was a GR-540-B/FOPZ-10316-A.

[Bob Gaines]

I seem to recall that a few years back, there was a mod swapping out the "guts" of our original electro-mechanical regulators with the "guts" from a new MOTORCRAFT solid state regulator.  That might help solve the ammeter problem  It was a GR-540-B/FOPZ-10316-A.

Some of the better reproduction regulators already have the solid state internals plus the correct vintage style base . Original base had a oblong hole in the base for the plug and the economy or modern base has a notch cut into the base. It is pretty visible if you know what to look for. One of the things I always look at when judging.  I think Virginia and NPD have a more concours quality and economy one to choose from.That is if you are concerned about historical details. The swapping out of guts is more work to do and retain the historical details . Not so much if all you care about is if it has a correct stamped cover.   

[kingchief]

OK, I made videos of my 1] current solid state voltage regulator, 2] a new solid state one and 3] an old-style reproduction of the original style [non-solid state] one. ALL exhibited the same jumping of the ammeter needle! So, my conclusion is the voltage regulator is not the cause. Hmmm. Now what???

Also, should the cover be glossy black or satin/flat black??? Thanks!

Cheers,

Steve

[greekz]

Have you considered the gauge itself?  If it is the original, it might be the problem.  Just a shot in the dark.

My '67 is just the opposite, jumps at idle and smooth at speed.

[Royce Peterson]

OK, I made videos of my 1] current solid state voltage regulator, 2] a new solid state one and 3] an old-style reproduction of the original style [non-solid state] one. ALL exhibited the same jumping of the ammeter needle! So, my conclusion is the voltage regulator is not the cause. Hmmm. Now what???

Also, should the cover be glossy black or satin/flat black??? Thanks!

Cheers,

Steve

The voltage regulator is not in the ammeter circuit. The voltage regulator is connected to the field on the alternator so if that doesn't charge obviosly the ammeter is only going to show a discharge. But it's unlikely to be the issue.

Anything that you do to a voltage regulator on the instrument panels will have no effect.

More likely the instrument itself is bad.

[sg66]

Couple thoughts,

1. Pull one of the wires off the gauge and put an ammeter into the circuit. If the ammeter jumps around, your gauge is likely fine. I forget if it's relevant to check both sides of the gauge but it's easy enough for a sanity check. See https://www.allaboutcircuits.com/textbook/experiments/chpt-2/ammeter-usage/

2. I believe it's a yellow and red wire connected to the gauge. Both come through the harness connected at the firewall. The metal on the connectors has been known to oxidize over time causing a poor connection so check those also.

[68blk500c]

Make sure the alternator harness is connected properly.