Mercury grand marquis whistle sound light dimming

Asked by Oct 06, 2017 at 11:22 PM about the 1999 Mercury Grand Marquis 4 Dr GS Sedan

Question type: Maintenance & Repair

When I drive the car sometimes I can hear a very
high pitched whistle sound, and when I use
electronics light the button that rolls the window
down Or turn on the radio etc. the lights slightly dim
for a second until I let go of the button, they only
dim when using electronics when the cars making
that sound. I believe it could be a loose connection
on  the battery but I’m not certain, need help, thank

1 Answer


I suspect the alternator. It would be good to measure the voltage when running, should be 14. 5 volts. Also, make sure the belt is good, and the tensioner. They can go bad. Some auto stores will check the alternator for free.

Your Answer:

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