Blowing backup light fuse

[skokie]

I have replaced all of the wiring under the dash. I got my brake light switch adjusted when I said well let see if the reverse lights work. I turned on the key and put it in reverse and it popped the fuse. Thinking it was a old fuse I put in a new one and it did the same thing. Is this a short? If so how do I fix it?

Thanks in advance

[Longhorn Man]

Yes, it is a short. You'll have to trace the wire from the switch to the bulbs.
A couple things to look at before inspecting the wire from front to rear...
check/replace the bulbs. If one is broken it could cause this, or even internally dammaged (undetectible) it could do it... 2 1156 bulbs will ensure they are fine, but for troubleshooting you can just remove the bulbs, pop it in reverse with a fresh fuse. If it blows, keep going, if it doesn't blow, replace the bulbs and have a beer.
Inspect the harness under the bumper... where it's been spliced 5 times for trailer lights. Also, if the bed has been off, look for the harness being pinched under the bed. You're looking for pinches, breaks, cuts, spaces where the wire has been rubbing on the frame or anything else... check it out, and repair anything found.
If it still blows the fuse, there is a slight chance the switch is bad... but not likely.

[skokie]

Thanks Andy. I will remove both bulbs and go for a new fuse. If this works since I dont drink I am going to rely on you to have the beer for me LOL

[Longhorn321]

Here is another trick...If you have a test light, check to see which side of the fuse holder is hot when the fuse is out. Then connect the ground clamp of the test light to that or another hot source and the test probe to the OTHER side of the fuse. With the reverse bulbs out, the light should not light unless you have a short. If the light does light, shake the harness and see if the light goes out. If it does, you are getting warm!

[Longhorn Man]

well, I don't do beer either...
have a dew then!

[skokie]

Ok I tried it without bulbs and it blew the fuse as well. I got under the truck and I checked all of the wires. The rear harness is a year old but the one that connects to that and runs to the front is original and very stiff. I am going to replace it and see what happens. Matter of fact it cracked a bit when I touched it. I didn't see any exposed wires on it though.

[Longhorn321]

Divide and conquer! If there are large chunks of the harness you can disconnect, disconnect 'em and see if the fuse still blows or if you don't want to keep popping fuses, do what I said with the test light. I don't know how much that harness is but I would isolate your problem before I threw money at it. Since your short is there all the time, it should be easier to find than an intermittant problem. Start disconnecting stuff until you find the problem. Then spend money!

[Longhorn Man]

yep, unplug at the frame on the drivers side by the rear bumper, try it again, if it blows, then unplug on the firewall on the drivers side, if it still blows, then it is under the dash