Everything has been working fine for the past few days since I got my '88 Mustang back from the shop.
It's equipped with a 130A alternator from Pep Boys and under-drive pulleys.
If you've ever run under-drive pulleys, you probably already know that the voltage drops at idle, but works OK when the revs are up. And that's the way it's been with my car...until last night.
I open it up on an on-ramp to the freeway. About halfway through it, I notice the "AMP" light come on, as if the car had died. But it didn't die. It was still running just fine. It was only on for a second or two.
On the freeway, I notice my voltage was down, about where it is when the car is idling. The AMP light doesn't know whether to come on of stay off.
With some playing around, I found the following:
- The voltage is down at idle.
- At 1200-2000 rpm it picks up and looks "normal".
- As the rpm goes above 2000, it starts coming down again and the AMP light comes on.
Those are the symptoms. What is the problem?
Bad alternator? Voltage regulator? Something come disconnected? WTF?
