Just a heads up to MGM owners regarding the Lighting Control Module (LCM). I 'd like to relate my experience with our 2010 GM bought late last year used w/57K miles. When purchased the interior lights, floor board lights, map lights, rear passenger reading lights, and interior trunk light did not work. Everything else worked - exterior lights, dashboard lights, horn, etc. Purchased an S&G Tool Aid #25100 Short Finder off ebay and some fuse "prongs" to see if I could find the "short". Slick little tool. Plugged it into the fuse slot for interior lights (LCM), F18 (15A fuse) - long story short, I could not find it.
After searching over the internet, came across Refurbished Light Control Modules: Ford Crown ,Mercury,Lincoln TownCar $89-90
. (midwestteckmart.com) They indicated that one of the LCM symptoms was the interior lights do not work because the B+ connection is bad. They sell a rebuilt LCM with 4 year warranty - costs $80 + $120 core charge (refundable) + about $10 core return shipping charges. I rolled the dice, purchased one from them, installed it and Bam - everything is working. The 2010 GM LCM p/n is 8W7T13C788CA. This p/n is apparently good for 2008 up. The module I received from them was marked for a 2013 Lincoln Town Car, so it apparently works for that one also. Their LCM had the same p/n as mine. Replacing it was very easy, took about 15 minutes total time to remove and replace. They included instructions on removal. Move the driver seat back as far as possible. It's located to the right of the steering column, behind the dash, just above the OBD connector. Remove 2 7MM Hex Head screws, slide unit towards firewall and twist to left or right to clear the mounting bracket, the 4 cables are long enough to allow the unit to drop down to disengage the 4 connectors. Reverse the procedure for installation. Their instructions indicated some models have an outer plastic cover that is held in place with a couple of snapin/snapout plastic rivets, mine didn't. The hard part was lying on my back on the floorboard. Anyways, I hope this helps someone in resolving their lighting issues.