Neither front nor rear fog lamps work on my car. The fuses check out ok visually. The indicator lights do not come on when I press the buttons. Everything else on that panel works. I had the radio stack out a few weeks ago and did not notice any loose connectors floating about, so I don't think that the lamps have seperate connectors that are unplugged, but I know I could be wrong. The front lamps don't show any signs of burn out but it looks like the filaments have covers over them.

Anyone know what the problem is likely to be?

 

Front lamps only turn on when the high beams are off, so just make sure they are off to eliminate that as a possibility on the front lights.

Both front fog lamps are protected by fuse #17 in the engine compartment fuse box. It's a 15 amp.

The indicator LED above the switch gets its power from the output of the Body Processor Module. In fact, the BPM is what actually powers the fog lamps. The switch just sends a signal to the BPM and then the BPM turns on the relay to the lights. The same signal that turns on the relay also feeds back to the LED on the switch, so if the LED isn't on then the BPM isn't putting out the signal to turn on the lights.

Soooo... I'd guess that either the switch pack has come unplugged (are the heated seats working?), or a connector has come loose on the BPM, or the BPM is bad.

The LED for the REAR fog lights works slightly differently from the fronts. It comes straight out of the BPM. The switch sends a signal to the BPM to turn on the fogs, and the BPM has two outputs, one goes to the rear fog lamp relay, the other goes back to the LED on the switch.

I'm still thinking the plug on the switch pack has come undone or the BPM is bad.

 

Problem solved! Maybe because it's dark now, but they are working fine now. I was testing them earlier while the sun was still up and they wouldn't work, perhaps that had something to do with it. I'm a little confused by the complexity of how they operate, but I'll sort it out later. Thanks for the help Sam!

 

AH! The fog lights won't turn on unless your headlights are on.

 

That's what happened then. This afternoon the car was in the garage, and I turned off the headlights so I could see if the fogs would shine against the wall. Needless to say they didn't, guess I outsmarted myself haha. In my previous 2000 XK8, IIRC, if you wanted the fogs you just hit the switch and they came on.

I always thought the idea was if you were in dense fog, the headlight beams would scatter so much as to blind the driver, so you used the fogs with the headlights off. How can someone do that with this setup?