LCM woes...

There is a black box, about the size of a hard drive, under the driver's side dash of all Ford Crown Victories and Mercury Grand Marquis made between 1998-2010. It is called the Lighting Control Module (LCM). This box controls all the lighting functions of the car, and does so predominately with solid-state circuitry except for a few relays.

This makes for a very compact and centralized control for the varied options and customizations that a police/taxi/fleet vehicle must endure. However, it was engineered with a flaw: The primary relays, one of which controls the headlights, are inadequate. Specifically the headlight relay is know to fail after about 4-5 years of use due to heat. It's a rather small, and poorly made relay which is unable to handle the amperage (up to 10 amps) for the low-beam headlights--especially in a fleet vehicle which may have the headlights on all the time.

What are the symptoms of a failed LCM? First, your headlights may turn off and intermittently. Next, they will soon fail altogether. When you attemp to turn your headlights on will no longer hear the small "click" indicitive of the little headlight relay doing it's job deep in the LCM. High-beam and other lighting controls will still funtion normally. As an aside: There are other hard to diagnose lighting problems that can be symtimatic of a faulty LCM. These include (but are not limited to): Failed dash lights; other lights turning off and on randomly; random buzzer noises; and complete lighting failure.

What can be done to fix a failed LCM? The LCM is easily removed and can be replaced with either a new one ($375-$510) from your Ford dealer, it can be replaced with a used one from a junkyard (but it may be faulty or soon sucome to the same problems as it's old), or you can rebuild it by replacing the faulty reley(s) with new ones (about $4 each).

Next: How to rebuild your faulty LCM...