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Electrical troubleshooting help needed!!!!!

Can Can

Can Can

Pusher Man
Joined
Feb 17, 2000
Posts
16,432
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Location
Cochrane, Alberta, Canada
This weekend I lost my brake lights and my parking lights. My signals still work all the way around the truck but my passenger side signal causes a very faded blink in the driver's side bulbs.

- If I replace the brake light/hazard fuse(15 amp), the minute I touch the brake pedal it pops.

- I tried disconnecting all the plugs to the rear lights to eliminate the circuit but the fuse still blows out when the brake pedal is applied when everything is unplugged???? /forums/images/graemlins/dunno.gif

Anyhow, automotive electrical is a mystery to me. It appears that I lost my lights after some light wheeling on some old forestry roads. Can someone PLEASE point me in the right direction as far a step-by-step procedure for solving this thing? Any hints or tips?

Thanks, brothers......... /forums/images/graemlins/1zhelp.gif
 
That circuit almost caused my truck to burn to the ground. I ended up with a dead short between the fuse block on the firewall and the tail-lights. Problem was the fuse box was damaged and the fuse didn't blow. /forums/images/graemlins/yikes.gif

Anyways, on the engine side of the fuse box there is a single bolt holding the harness. Remove that bolt and unplug the harness. The harness itself comes apart, and the tail-light part of it is the four wires on the far right hand side. Right hand if you're standing in front of the truck looking at it. Put the harness back together without the 4 wire tail-light part. Replace the fuse and see if it still blows. If not then the problem is between the fuse block and the rear of the truck (like mine was...) If it still blows it may be a bad brake switch, but you'll have eliminated the wires between the fuse block and the tail lights.

FWIW I ended running a new 4 wire harness to the tail lights from the block. I couldn't find the actual bad spot...

Rene
 
I had some wierd problems with this system as well. Check in the frame rail in front of the left rear tire. The wires run right there and it is fairly close to the exhaust and the cat. Mine were all melted from the heat and were crossed popping fuses. Hope this helps I had to do like Rene and run four new wires all the way back then I put them in some nifty heat sheild conduit stuff /forums/images/graemlins/waytogo.gif
 
If your truck is stupid and '80s like mine, that bolt holding that harnesses in happens to be one of the few metric fasteners on the whole truck. I think 10mm takes it out. /forums/images/graemlins/thumb.gif
 
It does sound like a direct short in the wiring to your back tail lights. If you have a meter, check for a hot wire that is grounded. Disconnect the battery and ohm each wire from ground to check them. Like they said, check all the wiring to the back for a cut causing it to ground out.
 
Also be very suspicious of any trailer hitch plug wiring--at my friends shop we had a similar dilema with a suburban and we pulled our hair out for hours trying to find the problem--after I had walked toword the rear of the truck,I thought I smelled rubber burning,I mentioned this to my friend and he agreed--further investigation revealed the rubber plug for the trailer lights was all gooey,like a gummy bear--and it was hot enough so you couldnt touch it--funny thing was it only blew the fuse once!--after we chopped the plug off,everything worked normally again--a new plug and the owner was off to the races--cost of plug,10 bucks- /forums/images/graemlins/smile.gif-diagnosis and labor (4 hrs!)75 bucks!. /forums/images/graemlins/yikes.gif
 
With Rene guiding me through the process over the phone last night, we were able to ascertain that the trailer plug was INDEED the root cause of the problems. Once I removed it from the circuit I stopped blowing fuses.

I still have yet to track down why I'm getting a goofy backfeed with the passenger side signals on but I'm pretty sure it can be traced to the wiring that runs along the frame rails. I need to spend a little more time with a test light to nail it down....... /forums/images/graemlins/deal.gif
 
What do you mean by a backfeed? As in, the turn signals are blinking together?

Every time I've ever had that happen, I had a bad ground. Fix the ground and it will fix that problem most likely.

Check where the body clips slip over the body. IMO this is a poor way to ground things as it is subject to corrosion.
 
The brown wire (courtesy lights) and the dark green wire (right turn/brake) are feeding power to each other. I figure there is a bad spot in the wires where the insulation is gone.

Example, you turn on park lights and the right tail-light lights up bright. You turn off the park lights and turn on the right signal light and all the park lights flash with the right turn signal.

Paul confirmed that power is finding a way from one circuit to the other using the test light.

Rene
 
It might be the turn signal switch too--or perhaps a bulb had one of its filaments break and touch the other one--this can cause a lot of weird problems,as does bad grounds.
I'm still trying to figure out why my 79 C10's wipers will suddenly come on by themselves,make one or two sweeps,then park,all by themselves,sometimes it will do it when I step on the brakes,other times whenever it feels like it(it has a goofy delay wiper factory setup)and then it wont act up again for months--I'm beginning to think its haunted! /forums/images/graemlins/thinking.gif /forums/images/graemlins/yikes.gif
 
[ QUOTE ]
It might be the turn signal switch too--or perhaps a bulb had one of its filaments break and touch the other one--this can cause a lot of weird problems,as does bad grounds.
I'm still trying to figure out why my 79 C10's wipers will suddenly come on by themselves,make one or two sweeps,then park,all by themselves,sometimes it will do it when I step on the brakes,other times whenever it feels like it(it has a goofy delay wiper factory setup)and then it wont act up again for months--I'm beginning to think its haunted! /forums/images/graemlins/thinking.gif /forums/images/graemlins/yikes.gif

[/ QUOTE ]

The checking Paul did was with the tail-lights not connected, so it removed them as a variable.

As for your wipers...that is really common on the 73-91 GM's with delay wipers. Mine did it too, but after I cleaned the 'park' mechanism at the top of the wiper motor with a bit of brake Kleen it stopped. Mostly the contacts just get corroded...

Rene
 
Thanks for the tip Rene--I'll add that to my "laundry list"of things to do to the truck after the motor swap is over--I actually heard it run last night--the power steering pump has been a real arsepain--the original one from the van the motor was in had a rotted resivoiur,so I swapped another one I had onto it,and hoped the pump itself hadnt been damaged from running dry on fluid(only ran it a minite or two to get the van off the trailer and into my shop to strip the motor)--well,the motor sounded great,(open manifolds! /forums/images/graemlins/grin.gifmy neighbors barking dog was getting on my nerves,after 5 years of listening to that mutt yapping 24/7,I needed some revenge! /forums/images/graemlins/smile.gifexcellent oil pressure, but I saw a huge pool of dextron leaking from the P/S pump--the resivouir I swapped onto it had a nice pinhole right in the bottom /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif--I took the pump off and brazed it with some brass rod with my torch--It almost caught fire,but I was beond caring at this point--today I have to put the Y-pipe on,and get a new tranny mount,then MAYBE this nightmare will finally be over for awhile,til something else goes wrong! /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/screwy.gif
 
[ QUOTE ]
As for your wipers...that is really common on the 73-91 GM's with delay wipers. Mine did it too, but after I cleaned the 'park' mechanism at the top of the wiper motor with a bit of brake Kleen it stopped. Mostly the contacts just get corroded...


[/ QUOTE ]

My '73's have to be manually parked. I was gonna get a new wiper motor but that's the only problem. How do ya clean the contacts (where)
 
The top part of the wiper motor has a plastic cover. Beneath that is the park mechanism.

Rene
 
Kewl /forums/images/graemlins/waytogo.gif.......thanks. I'll check it in da morin.
 
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