I have a ’99 supercab and have started having lighting electrical problems. Fuse #6 (Parklamps/Autolamps) fuse in the power distribution box under the hood keeps blowing and the headlights will come on by themselves without light switch on and will not shut off. The fog lights will work sometimes, but sometimes not. I took it to the shop and they could not make the fuse blow or find a short, but then when I drove away, the fuse blew. The truck does not have daytime running lights. I have replaced the light switch/fog light switch assembly, but continue with the same problems. All other fuses are ok. I replaced the relays under the passenger side dash today, but it did not fix anything. I even took both relays out and the lights came on without the switch turned on. The only way to get the headlights to go out is pull fuse #3 (Headlamps/Autolamps) to insure the lights don’t come on during the day and run the battery out, been there done that. Things are starting to get expensive and I am really getting frustrated. I really don’t want to take it to a Ford Dealership and pay them for exploratory labor. Can’t drive at night for fear of getting pulled over for not having parking lights. Anyone have any ideas or suggestions???

 

Cgray
I would suggest tracing the wiring from the headlights/park lights and see if there is any place the wire loom comes in contact with or close to a metal surface, edge, etc. Could be a wire (or wires) chaffing on a metal edge and makes contact while the vehicle is moving, body flexing, etc. Our mechanics @ my work had trouble similiar to this on one of our crown vics.....would only short out while veh was moving. We found a wire loom shorting against ground in the right fender well near the radiator support. The wires were chaffed.
Hope this helps.
Mike

 

I want to confirm, when you say the headlamps come on by themselves, is this regardless of which position the main headlamp switch is in ?
- To mean, if they are off, they still come on ( think that is why you are pulling fuse #3 ).

The items of note :

1. New headlamp switch = new autolamp on resistor and exit delay Rehostat.
2. Remove both the Park Lamp Relay and the Headlamp relay from the RPO relay block and the headlamps still come on.

Q1. Do you have a Remote Keyless Entry ( RKE ) on the truck from Ford ?
Q2. Do you have a alarm installed ( Ford / CodeAlarm or other )
Q3. Do you have a remote start installed ( again, Ford / CodeAlarm or other ).
Q4. Do the parking lamps come on, with or without the Parking Lamp relay installed ?
Q4.1. If not, what happens with the Parking lamps ?
Q41.1. Only blow fuse #6 if turned on, only blow some times, don't work, etc ?
Q5. Have you tried pulling Fuse #4 in the Central Junction Box ?
Q5.1. This is the fuse that feeds the AutoLamp moule, along with Remote Entry Module and Mirrors.
Q6. Have you tried pulling Fuse #29 in the Central Junction Box ?
Q6.1. This is the fuse that feeds the AutoLamp moule, along with the Transmission Overdrive Control Switch. We are doing this while the truck is sitting still, so no big deal with the O/D.

Just a few questions to try to whittle down if we are looking at a problem with the headlamps, or the headlamps and the parking lamps.

 

mgsalida & SSCULLY,

First of all, thank you very much for responding to my question. Secondly, for now my problem is fixed. Not quite sure what exactly fixed it for now. As I mentioned, I replaced the light switch and the relays in the dash. I also removed all the relays and fuses in the power distribution box and blew it out with air. I then replaced the fuse #6 and put everything back together and turned everything on and everything has been working for three days now. Again, I really appreciate your replies, and if this problem continues, I will definately try your suggestions.

I am glad I have found this website. I have learned a couple other things that have been bugging me about my truck that I have been able to fix too.

Thanks!!! cgray

 

No problem, Cgray. Glad you have "fixed" your problem!

Mike