I'm at a complete loss at the moment.

Went to start my truck (2003, 7.3 F250) one evening and I found the headlights on. No keys in the ignition and the truck hadn't been driven for 2 days. There was a strong smell of plastic and or electrical components burning in the cab. The truck started without a problem. I shut it off and the lights remained on. Cycling the MFS and light switch would not turn the lights off. I had to disconnect the batteries and leave it till time allowed for trouble shooting.

I've had it in my shop for three months now and this is what I've found so far.

-Source of the burn smell is coming from the fuse panel. More specific it's coming from a bulkhead that plugs into the panel. One pin connected to a White wire with 2 purple traces. I've traced this wire to one of 2 small relay packs in the engine compartment next to the driver side fender. I've replaced the relay this white/purple wire connects to as a precaution. This did not remedy my trouble.

-The local ford dealer told me this relay was for the A/C clutch. I located a 10amp fuse in position 10 and removed it. The headlights finally turned off.

-I started the truck and the A/C compressor clutch still engaged and ran. Smoke began to pour from the fuse panel once again. I killed the truck and head lights remained off. All done with the fuse in position 10 removed.

Here's where it gets weird!

-With the key/engine off and I turn the headlight switch on and MFS to low beam the fuel pump is running. Change the MFS to high beams and the fuel pump turns off.

I've looked over the wiring harness and there are no noticeable problems indicating multiple wires being shorted. How are all these issues related?


Thanks in advance for any ideas.

-Daniel

 

Have you pulled the entire fuse panel out and looked on the back side. Water intrusion corrosion could have started the problem and melted plastic is now allowing circuits to touch that shouldn't be

 

The fuse panel has been removed and all bulkheads disconnected. This is how I was able to identify the white wire w/ purple trace is connected to the burnt pin. Pics are below. No signs of water damage and or corrosion.

I guess my main question is how are the Low Beam headlights, A/C clutch relay fuse, and fuel pump related?

Thanks again,

Daniel






The white wire with purple trace is connected to this pin. It feeds to a relay in the engine compartment. This relay is on the drivers side by tte master cylinder.




The relay in question has been removed.