I have a 99 Grand Marquis and the headlights are turning on automatically and shutting off at any given time. Also the interior light is turning on and off too.All with the ignition off. Has anyone had this problem, and what can be done about it. Help! Thank you

 

The interior lighting in your vehicle is controlled by a Lighting Control Module (LCM). The LCM has control over the 2 lighting functions provided in your vehicle, courtesy lighting and demand lighting, in addition it has a battery saver feature that will turn off these lights and the headlights if left on with the key off. Erratic light operation would indicate the possibility of switch problems, wiring or the LCM itself is defective. Diagnosis of LCM problems is performed the easiest with a computer scan tool that connects to the communication port for the LCM. The LCM can perform self-diagnosis and report any problems found to the scan tool in the form of a diagnostic trouble code that can guide a technician in diagnosing and repairing the system. If you think that maybe you’ll try a used LCM from a salvage yard, there something you should know. LCM’s are programmable, they may look the same but the program in the LCM may not match. The only way to program a LCM is once again with a scan tool. Your best bet, get your vehicle plugged in. It’ll take the guess work out of the needed repairs.

 

You've proved helpful once again cpettymore7777 and I wasn't even looking for an answer!! My headlights started coming on by themselves too (although I noticed it only when the car was running). The problem began when I tried installing a factory radio from a 2005 Mercury GM into my 2003 Mercury GM. I had assumed it would work just fine, just a two year difference in the two radios and the connections were identical. I took the 2005 radio out again and reconnected the old radio and the problem disappeared. I guess the LCM is programmed for the radio as well?? I did notice when I had the 2005 radio installed the dimmer wouldn'taffectits display lightandthe"mode" remote button on the steering wheelstopped functioning. Maybe the dimmer switch or the "mode" button had something to do with the erratic headlights as well?? Either way, I hope I didn't cause any electrical damage. The 2005 radio was installed for a couple of months before I took it out and put the old radioback in. (By the way, if you're curious, the reason why I tried installing a 2005 GM radio in my 2003 GM is because I was after the satellite radio feature the 2005 GM's came with). Lesson learned: neverwant morewhen you have enough. Thanks again! Edited by: AngelD

 

When I had this problem I was advised to replace the keypad on the door. Worked like a charm. no problems since.