What causes the number 45 fuse to blow when you hit a hard bump or sometimes just by putting it in gear on a 2002 Ford Excursion?

Answer 1

Answer 1It really doesn't matter what the fuse number is. Any time a fuse "blows," it blows for only one of two reasons:

1. It is defective or,

2. A short has occured in the wiring of the circuit which that fuse was intended to protect. If replacement fuses continue to blow, that is a sure sign there is a short circuit.

The fact that the fuse blowing [or short] occurs only when there is jarring to the vehicle due to a bump, or movement of gear selector, suggests that the short is not there all the time, and is therefore what is refered to as an "INTERMITTENT" short.

To find the short, determine what circuit is related to that fuse, and then trace the wiring from the fuse to the end(s) of the circuit.

You will be looking for something like the "hot" wire being in contact with a sharp metal edge, where vibration has caused the insulation on the wire to have been "chaffed" to the point that the bare metal conductor wire has been exposed, and depending on the severity of a jolt, bump or vibration, allowed the energized metal conductor wire to come into contact with the GROUNDED metal.

Once the defect has been identified, the fix is to "reinsulate" the wire using a high quality "electrical" tape, or one of the "paint-on" wire insulating compounds. Good luck.j3h.

Answer 2 - A personal experience

I to had a similar sitiuation in which the two small gauge wires that run over the steering column and down the gear shift which power the overdrive off/tow haul switch rubbed through. I had to remove the plastic housing and cut/splice and heat shrink to repair.