Classic/Antique Car Repair: 66 Ford Mustang gauge spikes, ford mustang, correct voltage

Question
QUESTION: I recently replaced the regulator on my 66 mustang. since then, not sure if the regulator is the problem, only on an idle... at a light, etc., my temp, oil and fuel gauges all sweep up together to the high mark, then in time, come down together. the amps remain constant without spiking.  I already had my mechanic replace the regulator again, but no luck. Any ideas, or can you point me to another mechanic who might know? I myself dont know enough. There are no issues when the gauges spike, but I have had the car for over a year, and this is the first it has happened. I replaced the regulator because the amps were "twitching" to the right. putting on the new regulator has stopped that. But this gauge spikiing has me stumped.  Thanks. Al

ANSWER: Hi Al:
At idle, you could be getting a spike in voltage that is affecting your other gauges. Does she idle high? What are the RPMs at idle? If your idle speed is too high, it could be generating too much voltage, but I would think the voltage meter would spike a bit as well. Also, confirm that you have the correct voltage regulator for your car and that it is wired and grounded correctly.

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QUESTION: Thanks,  it isnt idling high, but I did have to replace the accelerator spring, the gas pedal is tighter now. we did wire and check all ground anumber of times. Is it possible something in the dash is doing it, is there a regulator for the gauges, or could the gauges be off center and no ground?

Answer
This is strange. It sounds like your regulator is kicking in to compensate for a low generation of power by the generator. Check your generator belt. Make sure it's tight and not loose or slipping. There is power to these gauges and the voltage regulator is designed to maintain a constant voltage to them at all times. The fact that it spikes at idle, could indicate the regulator can't control power to these instruments because the lead wire from the generator to the regulator is incorrect. What is your voltage on the car 6v or 12v? And what gauge wire is used between generator and regulator?