2002 F150 Screw 4X4 5.4
I have a problem with the fuse blowing thats controls the brakes, turn signals, and the emergency flashers.
After changing out the fuse:
1. the signals work
2. the emergency flasher work
3. hit the brake and blown fuse.

I think I read some where that the "BOO" could be the problem.
After changing out the "BOO":
1. all worked till last night. This was about 3 weeks ago.

Now I can change out the fuse and :
1. the signals work
2. the emergency flasher work
3. hit the brake and blown fuse.

I read some where that the cruise control release switch might come into play so I disconnected it but still have the same problem.

I have a topper on the back and I can't check the HMSL (High Mount Stop Lamp) if this yr. model has that? I can't remember if I can ever seen it come on. The 2 clear lamps (cargo lights) do come on when the door opens. The cap has a HMSL. May have to slide the cap off to check the one on the truck itself.

Also read that the power to the tail lights goes through the "MFS". (Multi-Funtion Switch). I feel that is where the problem is.

Really don't think there is a shorted wire cause that would blow the fuse as soon as you replace the fuse.

Any thoughts on how to check the "MFS".

Thanks,
Hump.

 

Probably a shorted wire AFTER the MFS, somewhere in the brake lamp circuit. I've never seen a MFS cause this issue.

Does the topper have any electrical wiring for brake lights? If so, start there. I'd bet the extension wiring is the likely problem area, especially where the wiring passes the transition point from truck to topper.

 

Thanks Pro.
I got to checking the the topper and found where the wires to the HMSL was pinched where the tie-down/clamp for the topper was. It didn't show any signs of shorted (burn spot/ arc) but when I replaced the fuse and check, all worked.
Crossed my fingers, this was the problem.
Hump

 

U might check the connection area of the wires running up to the topper, there may be a rubbed area where the wiring fab was done.

 

So far, so good.That was Tuesday. Todays Saturday. It went for almost 3 weeks before. Have not had to replace the fuse again. I will update later as to the status. I hope it's all good.
Hump.

 

2 weeks and still no problem. Well with the fuse. Now I have a bearing or something that is makeing a funny noise in the front end. Got to pull the front wheels and check the front bearings.
Hump.

 

I guess that can become a different thread to discuss.

 

Well it been a few weeks and all is well. No fuses have had to be replaced. Must have been that wire on the topper.
As for the noise.....it went away to.
But I did have to have the trany rebuild.
Hump