Mercury Grand Marquis electrical problem

[rcthiesen]

I have a 2002 Mercury Grand Marquis with about 85000 miles on it. Recently and for no apparent reason the head lights will come on and the horn will start blowing. I would start the car and it ran fine but we would not have dash lights or turnsignal lights. The seatbelt light would also stay on as well as the defroster switch light. After I disconnected the horn, I heard a shatter sound under the dash above the accelerator pedal and in the fuse box next to the battery. After much agravation I hit the box (looks like an electronic module) under the dash board and the lights went to normal. This is happening several times a week and it will happen while I drive or when I get in the car.

[Davescort97]

Welcome to Automotive Forums. Given all you say, it's probably a bad ground on the battery or a bad ground farther downstream from the neg. terminal. Clean the bat. terminals with a wire brush and reconnect. If it still gives you problems take the bat. out and check the individual ground wires.

[way2old]

Probably what you are tapping on is the Lighting Control Module. These go bad and do wierd things. The part is not inexpensive though. But by tapping on it and things work normally, you are close to the problem. You may unplug the module and place some di-electric grease in the connection to see if it helps.

[rcthiesen]

I have tried to reconnect and tighten connectors but the problem is still there. I have noticed that it happenes more in cold weather and after the car has been off for over 3 hours. After I run the car and warm up the engine for about 2 miles, I can hit the "what ever part it is" real hard and the system goes back to normal.
How can I be sure that my problem is not the Lighting Control Module and how do I go about getting the spec. for it?

[way2old]

There are a lot of tests that need to be done to determine if the LCM is the fault. Unless you have a shop manual or something like Alldata repairs, it is going to take a long time to test each wire.