I've been all through the Ford dvd and it sure is miserable compared to a simple book. As near as I can tell, there is a Lighting Control Module that is involved even when the car doesn't have the options you mentioned. This is just another case where the insane engineers had to hang an unnecessary, unreliable, complicated computer onto a circuit that never needed one before.
Logic would dictate that computer has an internal problem by your description of the symptoms, but before you assume it's defective, it can be accessed by the Ford dealer's equipment through the diagnostic connector under the dash. Given the age of the car, aftermarket diagnostic equipment used by independent repair shops should be advanced enough to also be able to talk to that computer. There are 12 diagnostic fault codes that can be stored in the computer although they are rather basic compared to Engine Computers and don't look like they will match your problem.
You can also check for corrosion on the computer's connector pins. There is a test procedure for "headlights always on" that ends with checking those pins, then replacing the computer. If a new computer is installed, the "configuration information" must be uploaded into the diagnostic equipment, then downloaded into the new computer. I guess they're assuming the computer being replaced is working. They also make reference to having to remove the accelerator pedal and shaft if the car has adjustable pedals. Good planning!
Given the computer's location under the dash, corrosion on the connector pins is a real good possibility. It wouldn't take much to allow enough current to trickle between two pins to make the computer think you turned on the head light switch.
Friday, January 13th, 2012 AT 12:36 PM