tail light fuse keeps blowing

[shadygrady]

Hey guys I got a problem and I dont think I`m gonna like the answer.One day outta no where my dash lights,taillights,and cig lisghter all quite.I replaced the fuse and it was fine for a day or so then it blew again.I`ve checked everywhere but cant find where it`s grounded.I`ve checked from the switch to the lights,replaced cig lighter and even driven around with the tail lights out and it still blew.If i wiggle the wires to the lights it will not blow.It doesnt always happen.I may drive around for 2 days fine and then out of nowhere it will blow after I hit a bump or it might blow everytime I replace the fuse.BUT,It only blows when I turn on the headlights/driving lights.I assume its in the wire somewhere between the switch and the lights but when its working properly I cant make it blow by shaking wires or harnesses.Sorry so long,but I`m stumped,and I cant drive at night.BTW its a 1989 Chevy k1500 THANKS

[pbouffard]

do yo have a trailer light plug on it? my 88 did and apparently the dude who had it before was killing it and the insulation was melted off the wires along the rear frame but didnt short but could have, i only found that when i removed the bed to paint my truck. unplug areas and try a fuse to help narrow down the zone. have you done any work in the dash lately?

[shadygrady]

Oh yeah,I forgot to mention that I removed it cause it looked like it had some pin holes in it that might be arcing.That didnt do anything.I just hope I dont have to strip all that plastic conduit stuff off along the frame and search every inch.I`m almost ready to just splice a wire in at the switch and run a new wire

[crabtruck]

Welcome back to the forum shadygrady, long time since Feb, you miss us?

The cigar lighters are common source of shorts as the truck gets older. Do you use it for anything on a regular basis?
Lot of sharp edges thereabouts as well, could be why bumps short you out.
Clock or radio have the same kind of exposure and I think are on same fuse, check that.
Try disconnecting the wire for lighter at the fuses, think it's just a stab connection at upper right corner.

Could be shorting at the switch itself, look or try banging the dash/switch there.
Did you inspect the wiring at the rear when you had the bulbs out ?
Not likely that the short is down in the loom somewhere, part of that protection the loom is for.
I'm betting your short is in the dash. Look extra careful where wires pass any sharp edge or screw.
If any work has been done in dash, likelyhood goes way up.

[Hayden]

Hey shady, Check the wires under the truck by where they run over the emergency brake bracket near the rear driver side tire. I had 2 trucks that did the same thing. the wires rubbed on that bracket so much it wore the insulation off and shorted out. Worth a look.

[shadygrady]

thanks for the replies fellas.I kinda forgot about this site.I asked a question bout an engine swap and I got no replies so I just thought maybe yall wernt as friendly as the other board I`m a member of for my Iroc.That is until I got an email wishing me a happy b-day the other day.I looked under the User CP and relized I didnt put I wanted e-mail notification to any replies that were posted to my thread.Oops!I`ve eliminated the cig lighter.I use it for my sirius satalite radio.It did have a bad wire on it but it kept makeing it either work or not work,not blow a fuse,but I fixed that.My stereo is hot wired to the fuse box cause I couldnt find a hot wire or acc wire in the dash.I cut and and taped up all the extra wires in the dash so I`ve pretty much eliminated that as far as what I can see in there.I took the switch out while it was working properly and couldnt get it to blow no matter what I did.Then an hour later I hit a bump driving down the road and it blew.I`m going to check again under the truck.I`m driving my car now so I dont get caught at night without tail lights,but I dont like putting all the miles on my car.I also removed the bulbs and checked cleaned all the contacts,then I took the entire tail light assembly out and drove around and it still blew.The cig lighter works fine till I turn on the lights and the fuse blows.But it doesnt always blow.It seems like after an hour long drive on the interstate it works for a day or two.then out of nowhere when I turn on the lights one day it blows.But for two days I turn on the lights and it doesnt blow.

[Streakn]

I should mention that when all else fails on finding a short on a semi, we would put in an oversized fuse, this allows the wires to smoke and shortens the time needed to find the problem. I don't suggest leaving in the oversized fuse for a long period of time though, unless you want it to burn.

[shadygrady]

Trust me,I am strongly considering a smoke test.

[tjzz4]

If you have more than one component on the same fuse it may be necessary to locate the splice where they are joined and install separate in line fuses in each wire to isolate the wire. Then...when it blows one of the fuses you can either locate the short or overlay a new wire form the splice to the component.
I always start by looking where there is evidence of tampering with the original harness as a likely spot for a short.

[Streakn]

The only other thing I can think of is perhaps you have something inside your switch causing the problem. Have you checked the switch itself? Whenyou shake it can you hear a rattle? It can arc power shorting the fuse out. Either that or go through your entire wiring harness. I've seen wires melt together and cause a surge, shooting the fuse. When all else fails, smoke it. Just be ready to put out the fire and pull the fuse.