Same 2000 Grand Marquis radio problem. Suddenly quit working after shutting off 3-4 times. Pulled radio, checked wiring harness and antenna plug in. Also checked fuse under the dash. All seem to be good. Is there possibly another fuses under the hood or it the radio done for? Thank you in advance.

Here is a wiring guide I found an my be of some help, hope it does. The top 3 listed, I would check first just because 2 require electricity an the last is a ground. Good luck an God Bless

2000 Mercury Grand Marquis Car Audio Wiring Guide

Car Radio Battery Constant 12v+ Wire: Purple/Light Blue Car Radio Accessory Switched 12v+ Wire: Yellow/Black Car Radio Ground Wire: Black Car Radio Illumination Wire: Light Blue/Red Car Stereo Dimmer Wire: N/A Car Stereo Antenna Trigger Wire: N/A Car Stereo Amp Trigger Wire: Blue Car Stereo Amplifier Location: N/A Car Audio Front Speakers Size: 5″ x 7″ Speakers Car Audio Front Speakers Location: Doors Left Front Speaker Positive Wire (+): Orange/Light Green Left Front Speaker Negative Wire (-): Light Blue/White Right Front Speaker Positive Wire (+): White/Light Green Right Front Speaker Negative Wire (-): Dark Green/Orange Car Audio Rear Speakers Size: 6″ x 9″ Speakers Car Audio Rear Speakers Location: Rear Deck Left Rear Speaker Positive Wire (+): Tan/Yellow Left Rear Speaker Negative Wire (-): Gray/Blue Right Rear Speaker Positive Wire (+): Brown/Pink Right Rear Speaker Negative Wire (-): Orange/Red