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2005 Mercury Grand Marquis - headlight issue

My wife has a 2005 Mercury Grand Marquis. With the light switch in either the Auto or On position the headlights do not turn on. However if she pulls the Bright/Dim switch and holds it tight towards her, the headlights come on. A local mechanic told her to replace the lights, but I cannot see all of them (bright and dim) going bad at once. I am thinking either the switch or Light Control Module. Is there a way to test these without blindly replacing one just to find out I guessed wrong?

Justin Nissen

If the lights stay on while fiddling with the switch, guess what? The problem’s with the switch.


When you pull the dimmer switch toward you this is called “Flash to pass”. This feature is powered by a different fuse than the headlight switch and illuninates both high and low beams.

When you push the multifunction/dimmer switch forward for high beam do the high beams light? If so you may need low beam bulbs. If not you’ll have to check the fuse, switches and module.

“Fiddling” with the switch gives no change whatsoever in the headlights, but thanks for your input.

Nevada_545 - The lights do not come on in the high beam or low beam position at all, they only come on in the “Flash to Pass” mode. I was assuming that the same fuses were being used in the Flash to pass mode. I will check fuses before replacing the switch or the Light Control Module.


I do not have a wiring schematic for your particular model but do have one for my Lincoln which also uses the Auto Lamp feature.

While there are probably differences in wire codes, etc and I won’t attempt to go through the complexity of explaining all of it as that could get mind-numbing, you might check the underhood fuse/relay box. There may be a 40 amp headlamp fuse that is blown; knock on wood.

Do the drl’s work? Could still be the multi-function switch. 15 is a separate output from the switch.

I reseat the connections at the LCM and all of the lights worked for about 5 minutes. I am able to repeat the lights working again by reseating the connections. I am going to replace the LCM and see what happens.

I’m having the same problem with my lights and I was told its the light control module. Do you think it causing my battery to not stay charged?

If you do indeed have the same trouble as the OP had then replacing the module should fix the issue with the lights. As far as the module causing a battery drain I doubt that it is but it is possible if power is applied to it at all times. If the power gets cut off with the ignition then I doubt that it is causing a problem with the battery. There are ways to find out what fuse path a parasitic battery drain is taking.

@Joe33, It would be much more conducive to sorting out an answer if your complaints about the light module and battery were confined to one separate post.

From your post about the battery it sounds like the battery may be weak. The light modules are designed to keep the lighting on for up to around 4 minutes or so after exiting the car and this length of time should not run a good battery down.

I have the same problem with my 2005 Grand Marquis. Started by replacing LCM (lighting control module) and then ALL relays in car. Still have intermittent problem. Next replacement will be headlamp switch. When lights do come on I can hear a “click” when turning switch, if it does not click the lights do not come on. Any thoughts?
Don’t know if this is related, but a few times when I used turn signal while changing lanes, there was a sizzling sound and radio came on. Could this indicate a short in the turn signal?
Thanks, DJ

I think the multi-function switch could very well be your problem. There is a lot going on with them and they can wear out.