Alternator excitation wire voltage pulsing

Asked by 70Olds Mar 06, 2021 at 03:12 PM about the 1994 Oldsmobile Ninety-Eight 4 Dr Regency Elite Sedan

Question type: Maintenance & Repair

I have a 1994 Olds 98 regency non-turbo. When the car is running the lights
pulse in a rhythmic manner. You can even hear it in the engine and how it runs.
I had the alternator rebuilt thinking it was a bad alternator as these cars are
prone to. This did not correct the problem. When you put an analog voltmeter
on the alternator excitation wire the needle pulses. This had the alternator
repair shop completely stumped. I’ve been told it could be several things one
of which is the computer. Any help would be greatly appreciated.

157,855

James answered 3 years ago

How does the alternator perform off the car? If it performs fine on the bench it's not the alternator but I'd have it tested somewhere else instead of the shop that did the rebuild. When something like an alternator is rebuilt the parts like the diodes and voltage regulator are tested and if they pass the test they're reused, not replaced. They might test fine on the bench but fail under load in the real world under the hood! I work at a local auto parts store and we get defective alternators and starters back all the time for that very reason. But if the alternator is truly good you need to check your battery cable connections at both ends. Make sure everything is clean and tight. Check the wiring at the alternator, same deal, everything clean and tight. Load test the battery as well. It may be failing. I had a similar problem on an old Pontiac and it turned out to be a loose battery cable connection at the starter. Hope that helps! Jim

Mark helpful