I have a 1981 Mercury Grand Marquis and it keeps loosing power after 20 minutes of riding. I have anew battery and alternator. I unhooked the radio, AC compressor, and fog lights. It still dies.

Asked by Oct 15, 2016 at 10:07 PM about the 1983 Mercury Grand Marquis

Question type: Maintenance & Repair

I have a 1981 Merc Grand. The previous owner put a 5.0/302 motor in it. There
are a few things that has been converted on the car such as the fuel filter now
requires a 1976 filter. The factory recommended alternator is no longer the one
that works for the car. What could the problem be?

2 Answers

1,155

It could be some wiring going to the alternator. Maybe it isn't getting activation power because of differences in wiring. Measure the voltage while running, if less than 14.5 volts, it's not working. One needs the circuit diagram for the car, and for the car with the alternator you're using, and a genius to figure it out.

58,815

Most likely the 1976 alternator can't keep up with the demands of the 1981 electrical system. An '81 Grand Marquis uses a 65, 70, 90, or 100 amp alternator. While a '76 Grand Marquis uses a 38, 45, 55, 61, 90, or100 amp alternator. There are 2 choices for the 90/100 amp alternator for the '76. One has a 9 o'clock terminal position and the other has a 12 o'clock terminal position. I'd suggest getting the 100 amp alternator. HTH. -Jim

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