Ok, so here is the deal... Walk out to my 02 f250sd this afternoon after it sat for 9 hours while I was working... the lights are on... look inside and the light switch is in the off position... HMMMMMM. Open the door and it smells like burning wires. Car cranks without a problem but lights will not go off. Unplugged light switch and still lights are on. Open fuse box and all fuses look good none of the relays are hot. Reach around to back of fuse box and almost burn my fingers. Remove 4 screws that hold box in place and look around back. Unplug the wires going into fuse box and see that one is melted and it appears it is melted inside the fuse compartment itself. I am not very savy with stuff like this but can any of you explain what might be going on inside this black box? Have any of you heard of this before?

Thanks for any help you can offer

 

Wow sounds like fire hazard. It could burn. I have had a problem with the headlight switch getting so hot it was melting. If it melts it could short. Since you can't turn off the headlights you might have the same problem. Difficult to analyze from a distance. NTSB (if I remember correctly) had listed this as an issue years ago on Ford products. Good luck and you might consider disconnect the batteries before you leave it. Jim

 

Definitely sounds like a fire hazard. You SHOULD disconnect the battery (negative at least) and have that unit looked at. For sure something is causing the wires to become hot enough to start melting the insulation and the conductors are probably touching a live source which is why the lights stay on.

 

Hmmmmm. This is interesting. Any wire that is too small for the amount of current it passes will get hot. It may be that normally this isn't a problem because the vehicle is in motion and there's plenty of cooling air around, but if the car is sitting still, particularly maybe under hot conditions, it melts the insulation.

The point is, either there is some defective part arcing (like a switch or relay), or the wire might actually be designed too small for the load......

It'll be really interesting to hear if anyone else has heard of this kind of problem...

 

The headlight switch becomes defective when it has a loose contact and generates a high resistance. The headlight draw a large amount of current. The heat/power generated is a relationship between the resistance and current necessary for the lights. If the resistance becomes 5 ohms and the current is 10 amps which could be easy for headlights. The power generated at the loose connector could be 500 watts which is more than enough to melt the switch and cause a fire due to the inability to dissapate the heat. Hope this helps understand the headlight switch that had the headlights on would be my first place to look. Granted there could be other things but my $.02 bet would be for the light switch. Jim

 

Thanks for the tips. I actually unplugged the light switch and the lights stayed on. Also, I am able to turn the switch on and the lights intensify.... hit high beam and they get even brighter. I ended up taking it to the dealership today and they are going to look at it. I will post with what the root cause was.

Thanks again for the input.

 

Was the plug deformed when it was pulled out,, if so it would indicate the plug overheated, just as a clue. Let us know what you find. Thanks for letting us know of this issue. Jim

 

Look for evidence of a water leak in w/s and pillar area. My '04 had a leak at the pinch weld at the top of the door opening, and it dripped right on the back of the fuse panel/gem module. (Now called a "smart junction box"). We see that once in a while, can cause all kinds of strange electrical gremlins.

 

Well, Ford dealership called today and indicated that this was going to be covered under the recall of the switch that is located under the brake fluid tank... it escapes me the exact term he used. He indicated that this was the first time they had ever seen this result from the defective switch but after they tracked it down it made sense.... good for me because he indicated that the entire engine wiring harness had to be replaced because of all of the damage the short did....

Thanks again for all of the help with this deal

 

There is a recall for gasoline engine cruise controls for a potentially defective switch that can cause a fire.. NTSB has a record. Perhaps that's what they found on yours.

 

Hello I'm having the same trouble on my F-250 diesel that started last night getting home. Smelled buried wire a little. Turned off the light switch,and everything but the headlights turned off. I unplugged the switch and they still stayed on. Finally hard to pull the fuses from the box under the hood. That's the only thing I had time for last night. Gonna try it again today after work. Dose anybody have any ideas?? Thanks

 

I have a 7.3 super duty 4x4, automatic if that helps