At idol speed my dash lights and headlights dim. (1987 Towncar, 5L engine) When motor speeds up they get bright again. Thought it was the alternator so got a rebuilt one from NAPA. 3 weeks later the problem still exists. Now the alternator does not charge at any speed. Car has new battery cables and coil.
I have noticed that the electric door lock on rear door clicks buy itself occasionally.
Why would lights dim significantly at idol speed?
If there is some current drain or short wouldn't it affect the current at any speed?
If there is some current drain, would it cause the alternator to not charge at all?
Will a new alternator be more reliable than a rebuilt one? (The NAPA store said they have as many new alternators returned as rebuilt ones)