2003 f150 supercrew with 166,000 on it. Daily driver. Keeps randomly blowing 10A fuse under dash that controls ABS\4×4\turn signals. No routine causes. Just blows at random times. Fuses were blowing instantly upon replacing then stopped. Doesn't blow when turning switches for turn signals or when turning it to 4x4. Just does it randomly. Sometimes will go months without blowing. Tore dash apart and can't find any wiring issues there. Could be somewhere else? Is ABS\4×4\turn signals going bad?

 

What is the fuse # and which fuse box (see owner's manual)?

This is basic information to provide if you want help.

 

It is fuse number 23 under the dash. 10 amp fuse

 

I am looking at the diagrams. Thinking what could be in harms way that could be blowing the fuse.

Do you have shift on the fly 4x4? If so, there is a hot wire(white/lightblue) that goes down to this solenoid from fuse 23, and it's hot anytime fuse 23 has power. The GEM module grounds the other side of the solenoid to make it do it's thing, so if this wire was rubbed through somewhere underneath, you would not have to be in 4x4 for it to blow the fuse. They call it a "center axle disconnect" solenoid.

This fuse feeds several other things, but most of them are in the dash and should be out of harms way. There is a trailer tow battery charge circuit, another circuit if you have regular 4x4, the flasher circuit, the abs circuit. But they all seem to feed relay coils or other components under the dash or under the hood. The one I described above seems to be the only one that goes underneath the truck, were possibly it could get damaged easily.

 

oops, wrong fuse box in initial reply.

There won't be an easy diagnosis on this one since it's intermittent.


Unless it fails full time, it will be a bear to figure out where the fault is at. This would be one of those times where I'd tear the circuit apart at the splice(s) and install individual fuses for each branch circuit so the individual branch can be isolated. It's a lot of work but it's less work than tearing the whole wiring harness apart to find the problem.

 

I looked it up again. Underdash fuse box is F2 and it was fuse 23 10 amp? I think I got it right didn't I?

 

Yeah, you did. I saw the "23" and incorrectly assume it was the common (F1.)F23 issue that causes a dozen or more fault codes, but that fuse is in the other fusebox. I put the disclaimer there in case someone saw the original post before I changed it.