Blown Fuse

[Northrunner]

My truck keeps blowing the 10 amp back-up light fuse. I put a new one in and it works for a day or so and then it blows again. What's the best way to track down my problem? I've looked at the wires under the truck and don't see any bare wire causing a short, but there must be a short somewhere?

 

[Alan Reagan]

I'm assuming you haven't added additional backup lights. If nothing is jumping out at you as far as broken/burned insulation, take an ohm meter and connect one leg to either the B/U light pin in the trailer connector and the other leg of the meter to a good ground. You should read a fairly high resistance ( in the kohm range). Now with someone watching the meter for you (since the leads aren't very long), start from the rear of the truck and wiggle the wiring harness, moving along the frame. Pay close attention to where the wires break out of the harness or are attached to the frame with supports. If the meter suddenly begins jumping to a low reading (anything out of the K ohm range) you have probably found your problem. Also, check the backup light activation switch and make sure it's not cracked thus causing your short.