I just picked up a nice lifted 89 full size Blazer a couple of months ago and it has been great. All of a sudden it started blowing the tail lights/courtesy fuse. The interior lights work fine when I replace the fuse but as soon as I pull the headlight switch it blows it. I just replaced the headlightlight switch and it still does the same thing. Truck runs fine and everything else works fine. The only other curious electrical thing is that the turn signals blink really fast even but if you put on the flashers it blinks at a normal rate....hmmm... I already looked at all of the bulbs and holders, unplugged all of the rear light connecting wires that are by the rear bumper, and tried to follow line but with the mud I did not see where they all went... Any help would be appreciated.... oh brake lights work fine..... Thanks !!

ohhh forgot to mention that headlights work fine too...

 

Sounds like the wiring has shorted out somewhere.

 

Yes I know there is a short - does anyone have a wiring diagram ? or is there a place that is a common problem area that I should look at first ? Thanks agin..

 

You should check the wiring harness anywhere that it goes around a corner or near the sheetmetal. One place that can be a problem is where the wiring for the back of the truck goes down to the frame under the firewall. If the body mounts have sagged, the wires can get pinched.

 

^^^ also check where the wiring harness goes through the frame rail @ the front.

i noticed a few bare wires on my 'Burb there.


you also need to dig through the mud, see if that's where the damage is. a bare wire(s) in there could be the whole issue.

keep us posted on what you find.

 

Have a look around where your hitch wires are if you have any. Alot of guys just use electrical tape when they install hitches and wiring, and that tape could have come off where the trailer wiring taps into the trucks lights.

 

Thanks for all the hints - Just got home from work - I will dig into it Saturday and let you guys know what I find out.... Again I appreciate all the information....

 

I might be able to scrounge up a wiring diagram for the exterior lights if I can get a chance. I'm going to be taking down some trees tomorrow...

Oh yeah...

*Moving to Fullsize Tech*

*EDIT*
No time like the present. Please find the diagrams attached:

 

also check and see up underneath the dash and see if your wiring has been "hacked". i've seen a lot of the older chevy trucks that got "messed" with and people that didn't know their s*** tried to to fix stuff. adding splices , wire nuts, etc. mines the same way. getting ready to re-wire the entire inside fuse block.

 

OK I had some time today to work on tracking down my short in the wiring system. I took your advice and wired the running lights on a seperate switch so I can drive the truck again. Now the problem has shifted.... The fuse for tail lights/courtesy lights still shorts out.. UGHHH !!Looks like the problem is in the interior. The fuse only blows when I pull the headlight switch...So now I have no interior lights or dash lights. The weird thing though is that when I pull the headlight switch the dome and floor lights come on very dimly....and that is with no fuse in that circuit.... Any ideas where to look now ? I did disconnect the dome light at the plug in source at the fuse block and that eliminated the dimmed lights but the circuit still blows a fuse when I put one in..... Thanks again for everyones help...