I need some suggestions/help. My 2001 F550 powerstroke parking light circuit melted and I don’t know why. When I bought the truck it had some strange stuff going on with the lights on the flatbed being dim. Then one day it the parking lights and instrument illumination didn’t work. I checked all of the fuses and they are all good. I pulled the light switch to find all the burnt wiring. All the wiring from the head light side of the switch is burnt all the way up until about 4 inches from where it disappears into the main dash harness. I pulled the dash out figuring that I’d find more burnt wiring and I haven’t. Cant find a reason for the wires to be burnt in the first place. Also I pulled apart the switch and it looks good inside. I removed every light and wire on the flatbed to start fresh. Didn’t find any shorts there. Even with everything connected I can’t get any voltage to the running lights. Does any one have a suggestion for a possible burnt up black magic box somewhere that would make the parking lights not work? Suggestions on what may have caused the wiring to burn up?

 

The running lights on the flatbed you mentioned, how many are we talking about and what technology are they? Meaning are they incandescents, LED's, or something else? The headlight circuit on these trucks isn't exactly the best design. It's almost borderline too small for the factory configuration, plus the fact there isn't any isolation relays so all the power for exterior lighting has to go through that switch. It's gotten somewhat common for people to reconfigure the system by adding relays to lighten and divide the load on the switch. The concerning part here is the fact that no fuses are blown. This kind of thing is their exact purpose, so the question is why didn't they. The first thing that comes to my mind is someone broke the biggest rule about replacing fuses that have blown, and that's always use the correct rated fuse. I'd start by digging out your owners manual to compare what is supposed to be there with what is there. If that isn't the case then I'd be wondering if someone somehow bypassed the fuse block when wiring some of the aftermarket lighting allowing the circuit overload without popping the fuse.

 

The running lights on the flatbed are all the trucklite brand LED lights 2 on the forward corners of the flatbed. 2 on the back of the corners of the flatbed. 3 in the center and 2 led trucklite brand stop/tail lights. It’s not lite up like a chicken truck. There aren’t any other accessories on the truck. Stock radio etc no mods of any kind. I will check the fuses for size again but I’m pretty sure they are all proper which is why I’m currently on this forum.

 

Check trailer wiring, including truck splice box at end of truck frame, truck side socket, trailer side plug, trailer splice box on trailer tongue, and entire trailer.

Look for anomalies where the circuits could inadvertently backfeed each other.

 

Thank you both for the help. After carefully examining the fuse diagram I found that the fuses were over sized for the parking lamp circuit. So I replaced my burnt up wiring and completely rewired the flatbed and trailer wiring plug. At this point I believe that the flat bed wiring and the trailer light plug wire was the cause of the short and the oversized fuse is what allowed the wiring to burn up. After a couple of hrs of run time the wires are still nice and cold. I now will be checking for proper fuse size every time I buy a used rig. Thanks again for the help.