On a 2005 Grand Marquis the tail lights do not work but the brake lights work All fuses are ok What could the problem be?

Answer 1

Lights Don't Work

Without doing a "hands on troubleshooting" of your vehicle, no one can tell you what specific defect is causing your problem. Therefore this answer will of necessity be generic in nature.

Usually this type of problem is caused by what is called an "open circuit" condition.

Open circuits can be caused by several things, a few of which I can recall right now:

• A disconnected, or loose, connector [or splice] anywhere in the circuit.
• Corrosion, or road film buildup, on the metal contacts inside of any connector within the circuit.
• Corrosion on the the metal contacts inside the"socket" that the lamp [light bulb] is inserted into.
• A cut or broken wire anywhere within the circuit.
• IF complete and proper troubleshooting of the dysfunctional circuit does not reveal any of the above as causal, then it is possible that the switch [or relay if so equipped] is defective. As main lighting switches are very expensive, and difficult to change out, I suggest that switch replacement should be the last resort after all other causes have been eliminated.

It is very disconcerting to replace an expensive and difficult to install component only to find that is doesn't solve the problem, AND to find out later that the problem was caused by something else, and that here was nothing wrong with the replaced component.

So, do a thorough investigation of all the connectors, connections, splices [if any], and all components of the nonfunctional light circuit(s) BEFORE replacing anything.

I would first check all the connectors in the wiring harness [loom] starting at the rear light assemblies, working forward to the main [headlight] switch.

The "proper fix" is for someone who knows what he or she is doing to troubleshoot the nonfunctional circuits, find and identify the specific defect, and properly repair it.