Got a 2001 Supercrew with a Lightning front end. Just the other day the fog light on the passenger side went out. Checked the bulb - OK. Checked the voltage from the wiring - registered 11.94. Took the fog light housing with bulb and hooked it up to an inverter - OK. Yet when I hook the fog light up to the wiring, it WON'T WORK!!!

Anyone have an idea what is going on here???

 

Might be a problem with the socket. Have seen them get corroded. did you check voltage inside the socket with the bulb out?

 

Mine is the 1999-2000 style fog light that uses an H-3 bulb (one with the little pigtail coming off of it) - not really a "socket" - just a hole and clip that holds the bulb in. I removed the fog light with the bulb installed and hooked it to an inverter and it worked fine - I also switched the fog lights and both lights work on the driver's side and neither work on the passenger side. But like I said, I checked the voltage on the wires and it was very close to 12V.

 

One lesson I learned a long time ago is that "almost all weird electrical problems are a bad ground." Have you tried that?

 

The ground is part of the factory wiring. I am beginning to think it might be my connectors that I am using to attach the wiring to the fog light housing. That is the only thing I can think it might be, even though I am showing ample voltage coming thru those connectors.

 

Don't forget to try the highly scientific "wiggle test" to find this kind of problem. I've pulled my hair out for hours tracing wiring problems only to have a simple wiggle of the harness show the problem right up.

 

I would be willing to bet its the connectors. If the bulb is good and your getting voltage from the supply wires the connectors are probably corroded. You might want to try putting some dielectric grease on connectors that are exposed to the elements. You can get it from an auto parts store and it helps reduce galvanic corrosion and oxidation. Good luck.

 

in AC, weird problems can also come from a bad neutral

 

Just an update - replaced the connectors (speaker-type) and the voltage actually dropped - still no light!!

 

OK - still trying to figure this out:

1) Would a voltage of 11.95 keep a 12 volt fog light from firing up??

2) On an H-3 bulb, the wire that comes out of the bulb - is this the "power" wire (positive)??

3) When connecting a voltmeter to the fog light wires - red lead to the "positive" wire and black lead to the ground wire, should the voltage be reading -12.00 instead of 12.00??