[GrandMarquis_2000]

We had the same problem. It progressively got so bad the car engine wouldnt start at times, and it would idle *very* rough. We brought it to this mechanic and he fixed just fine by resetting the onboard computer. He was preplexed, we were preplexed but its been an year and a Canadian winter since then and we've had no problems.

About the voltage meter, the voltage drops before the car shuts down simply because the engine's revs go to zero. The voltage dip whenever you use an electrical device is due to the finite amount of current the alternator can provide.

Of note, when you lower the windows the voltage dips. But when the windows are fully lowered (or raised), the voltage drops even more. Stalled electric motors draw more current, so this is expected. The car design should not allow the motor to stall... but alas the electricals in the Gran Marquis are of fairly poor design.