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tail light signal issue

Justin Fleming

Justin Fleming

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So I was trying to chase down a tail light issue on 1990 k5. What I have found with a test light to ground is that the yellow wire is the blinker for the driver side, as the test light flashes with the blinker switch in position, and it is also the brake light for the driver side as the test light goes solid.

What color wire in the 4-wire harness should the passenger side blinker and tail light be? I am right up at the fire wall and no other wire in the 4-wire harness can I get the test light to blink when putting the test light on it or go solid when the brake is applied. So I am assuming the issue is at the main connection at the fire wall.

Any advice would be appreciated.

thanks
 
Looked at a diagram I have in a Haynes manual--says the rear lamps wires are as such:

Brown = parking or running lamps
Light Green = Left directional & brake lamp
Dark Green = Right directional & brake lamp
Yellow = Back up lamps..


I think you may just have a bad flasher,if no wires turn up bad..
 
I am 99.9% sure that my left blinker and brake was the yellow wire? Does not match up to your colors/sequence listed....
 
What year & model is it?..fleetside or stepside ?...
I am pretty sure GM kept the wiring the same colors from 1967 to 87,but there might be variances ..
 
diesel4me said:
What year & model is it?..fleetside or stepside ?...
I am pretty sure GM kept the wiring the same colors from 1967 to 87,but there might be variances ..
Click to expand...

It seems as if I wiggle the wire harness and or mess with the wires at the fire wall I can get the blinker to blink extremly dim and sometime it will bright for a blip of a second etc. Some gremelin somewhere...
 
Might be the connector where the wires pass thru,it could have corroded contacts in there..
My wiring diagrams only go up to '84,but "should" be the same..

Edit..found this on google images--looks like my manual has the wires wrong,which isn't really a big surprise--its been wrong before!..:surepal:

download (19).jpg
 
Yellow is always left side on these and most trailers, right is always green. Easy way to remember, yellow dividing lines on left side of road, green grass on the right. Check your grounds.
 
Justin Fleming said:
So it ended up being a dirty connection at the fire wall harness connector
Click to expand...

Well I thought I had it fixed then the fuzz pulled me over.....

what I thought was a dirt connection did not seem to fix the issue at had. The sogga continues....

So my guess now is that is that it is a ground wire. Does anyone know where the ground splice is? Inside my passenger rear tail light body panel there is a ground wire. I am only having the issues with the passenger side rear. Those grounds that I could find are good. Is there another splice point for the ground?
 
Did you pull the actual tail light "bucket" off the truck? Sounds like you did, just confirming. If you did, did you remove the ground, clean it, and coat with dielectric grease before reassembly?

No butchered trailer wiring to cause issues?

I can only think of the one ground behind each housing.

FWIW, my truck has an intermittent failure of one of the rear lights, and I've had the stupid thing torn down multiple times to try and fix it. I know it's in the socket, but no matter what I do, to include making sure the contacts are actually making contact, eventually it starts misbehaving again. At this point if I can find another one, I'm going to replace the socket assembly.
 
dyeager535 said:
Did you pull the actual tail light "bucket" off the truck? Sounds like you did, just confirming. If you did, did you remove the ground, clean it, and coat with dielectric grease before reassembly?

No butchered trailer wiring to cause issues?

I can only think of the one ground behind each housing.

FWIW, my truck has an intermittent failure of one of the rear lights, and I've had the stupid thing torn down multiple times to try and fix it. I know it's in the socket, but no matter what I do, to include making sure the contacts are actually making contact, eventually it starts misbehaving again. At this point if I can find another one, I'm going to replace the socket assembly.
Click to expand...


Yea all the basics are covered, new ring terminal, clean ground surface, dielectric grease, trailer harness is a plug connections type,no botched connections. Ground was verified by running a hot test lead from the battery thru a test ligth to ground wire....
 
Dorian and Justin, all I can offer is a problem I had several years ago with my old Torino.
When I would turn on the headlights, the turn signal indicators in the dash would light up dimly.
Worked on it off and on for a while. One day I discovered the ground contact in the front turn/parking lights was corroded.
I cleaned them up, put on some diaelectric grease and that seemed to fix the problem for a while
But it came back.
Back then, I did not have the aftermarket resources we have today, so I went to the junkyard and bought a used socket.
It was corroded like mine, but I cleaned it up and it helped.

I was puzzled as to why only the ground was corroded. The other two contacts were fine.
When the problem came back again, I tried touching a grounded wire to the outside of the bulb in the socket, and that stopped it. Hooking the socket ground to a known good ground did not.

Finally I cut apart the molded plastic socket I had taken off and found the real problem.
The ground wire was not well crimped onto the ground contact inside the socket. That caused the contact to overheat, which caused the corrosion.

Apparently it was a large production problem. The one from the junkyard was the same way, and I wound up fixed 6 or 7 friend's cars with the same thing. I think most of the Fords that came out in 75-76 had the trouble.

I cut the two sockets open with my Dremel tool, and soldered the connection. Then used some Plas-T-Pair to fill in the hole.

That fixed my problem, and I got pretty good at that repair over the next couple of years.

In your cases, I would replace the sockets. You might be able to check by tugging on the wires while the power is on.
That worked for me on other cars later on to verify the problem.
 
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