04 Grand Marquis...should be same as a CV. Tail lights sometimes do not come on. Dash lights do work. Does the same relay inside the LCM control both? Does anyone have a diagram of the 4 relays that shows which relay controls what? I did an external repair of the headlight LCM relay a few years ago before the recall (soldered in a pigtail with a full size relay on the outside of the LCM). That's never given any more trouble and local dealer refused to replace the LCM under the recall when the tail lights began to malfunction since my headlights work. I don't know if the recall to install an LCM bypass (which seems to be mandatory for them) would solve my problem or if I should look elsewhere. I have been able to wiggle the wires to the LCM and make the tail lights come on in the past. Thanks for any answers.

 

The recall will not fix your issue, since you use to be able to make them work by wiggling the harness I would have someone watch the tail lights while wiggling the harness little by little, if they come on wgen you wiggle a certain area you should open the wiring harness in the area and check for damage to the harness.
Does your license plate lights work? If yes the module is provided voltage, parking lights and license plate lights have the same source of voltage.
Does your brake lights work? If yes the ground is good since it is shared between the parking lights and the brake lights.
Below is a diagram with the supplied voltage circuits circled in red.

 

Thanks for the reply, Scott. I should have posted but actually forgot I had posted about it. I solved the problem by finding that the wiring plugged into the LCM was not in far enough to click in place. I found that because the local Ford dealer here in Jasper, TX really screwed the pooch when doing the newest eleven wire recall. After having the car for 4 hours, they called me and said they had it ready..."But your headlights don't work." The recall was for one thing only: to bypass the LCM headlight relay and make the headlights work. "We'll be glad to trace down what is wrong and fix it." I knew that song and dance. Pretend to find something, slap a charge on it. I told them it was something THEY did wrong, so I'd take it home and trace down their work and find out where they messed up. Sure enough, after a lot of painful lying on my back checking all the connections where they cut and spliced, I found that they cut and spliced one wrong wire. The instructions on the schematic for installing the recall in RED in the center of the page gave instructions for 2003-2004, and for 2005. My 2004 was wired per 2005 instructions. I undid their wrong work, cut the proper wire and spliced the ends and soldered them, and everything worked fine. I recently had bought my wife an Escape so she could take it to the dealership here when/if I'm no longer kicking. I'll probably be selling it and getting a vehicle she can take to a reliable dealer. "If you want something done right, do it yourself." Never more true.