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Ron, ASE Certified Technician
Category: Mercury
Satisfied Customers: 36034
Experience:  ASE Certs and Ford Certs
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We have a 2003 Grand Marquis. In June we found the back

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We have a 2003 Grand Marquis. In June we found the back lights were not working (the brake lights and the directional lights worked). At just the same time a recall notice came. The lighting control module (LCM) needed to be replaced. When I called the dealership to make an appointment about this, I asked them if the problem we were having with the rear lights was related to this. The representative said "no" and gave us an appointment sometime in the future. In the meantime, we went to a neighborhood mechanic who put in a new switch. The back lights then went on for a short time, but then they went off again. The appointment with the dealership was a day or two later, so we brought the car there. We told the dealership representative about all of this, and he said that everything was related to the LCM covered under the recall. When they finished work on the car, he told me that everything should be fine now and something to the effect that they "rewired everything". Now, over a month later, the back lights are not working again. I have three questions:
1) What do you think the problem is with the back lights?
2) Do you think it is related to the LCM?
3) Do you think I should go back to the dealership about this in view of the above story?
Thank you!

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

Customer: replied 1 month ago.
OK, thanks.

Your reverse light do not run through the LCM and if they are now out again with a new switch then I would start first with making sure the F2-16 fuse (15AMP) located in the interior fuse panel is okay and has power in and out of it and if that checks okay then take is back to your mechanic and have him recheck the new transmission range switch that he replaced to be sure you have power in and out of it to the reverse lamps.

Customer: replied 1 month ago.
Thank you very much. What do you think the dealership mean when they said that they did a complete rewiring and that it would take care of everything? What's more, they obviously checked it.

Im not sure what that means because there is no rewiring required when they replace the LCM. That being said your reverse lamps are not ran through the LCM as well so start with checking the fuse I mentioned and if it checks okay the have the new switch checked.

Customer: replied 1 month ago.
OK, thanks. When you say "switch" are you referring to the console switch that I turn (this was replaced at the dealership) or are you taking about an internal switch that I can't see?

No, your reverse lights are controlled by the power from the Fuse F2-16 out through the transmission range switch located on the driver side of the transmission. I am assuming that is the switch he replaced since that is the switch that controls your reverse lamps.

Customer: replied 1 month ago.
you mean the visible from the outside?
Customer: replied 1 month ago.
I mean to say, the switch is not visible from the outside?

Yes it is , see the link below for its location. It mounts to the side of the transmission.

Ron and 3 other Mercury Specialists are ready to help you
Customer: replied 1 month ago.
Thanks, again.
Customer: replied 1 month ago.
Hi Ron,
I see you are online. The mechanic kept the car overnight, and the next day the lights went on normally. He didn't do anything. He said to wait and see. What do you think?

If there working as designed then it dose make it almost impossible to diagnose so I would agree with him. At this point the best thing to do is wait till they fail again and then run the test steps to verify what has failed.

Customer: replied 1 month ago.
Thank you very much.

Your very welcome and thank you as well.