How do I fix an inoperable automatic trunk release on a 2003 Mercury Grand Marquis?

Here is your Fuse Box Diagram.

Mercury Grand Marquis (2003-2011) fuses and relays

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The fuse box is located under the left side of the instrument panel. The location of the fuses in the passenger compartment: Mercury Grand Marquis (2003- ...

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You have a short between the trunk motor and the reverse lights. Follow the harness from the trunk latch to to reverse lights. Open the harness there and start looking.

Usually what causes this is your reverse clutch is worn out in the transmission, or there is a bad valve

Sometimes you will find a button inside the Glovebox. This is an Electric trunklid release. Some of the models had controls on the lower drivers door along with the Gasflap release. It depends on the Series that you have. The S, and GS, had less features than the LS model.

You can go to a Locksmith and they have a box of keys and will try them until one opens your trunk. Then you can have a key made to match your lock.

I don't believe the inside releases were made standard in 1992.

The carpeted trunk panels are held on by Velcro on each side and 2 or 3 plastic twist nuts on the bottom panel. The light sockets are behind the carpeted panels and you twist the socket fixture and pull it out of the back of the tail lense.

change the lock actuator on the trunk latch

on the grand marquis there is a button in the trunk to reset the pump it will be in the fender weld. some models it is in the glove box but they r usually in the trunk

What speed?
In the trunk area?
Around the rear doors?
Only in crosswinds? Sometimes the antenna makes a whistle noise in cross winds at 50 plus mph.

Get a roll f 2 inch masking tape, and tape off areas one at a time and test drive.

It is in the trunk I can remember which side on a 92 but it will be behind the side trim panel almost straight down from the trunk hindge.

10 year old remotes go bad often, especially due to moisture retention.