Brake Light Problems

[Boone83K10]

on the diagram you provided, it shows a ground on the passenger side... mine has no such ground.

 

[chengny]

That's because the rear lighting diagram I posted was for a Suburban - sorry couldn't find a CK fleetside at the time. Here is some stuff that might actually help:

A complete rear lighting harness recently pulled from a 85-86 1/2 ton Sierra Classic fleetside. It will be identical to yours (except maybe the license plate lighting)

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And the correct rear lighting dwg for your truck:

 

[Boone83K10]

Ok I got the trailer harness off. It was using two wire splice caps and then redundantly wrapped a 2nd time around bare wire above the splice. I undid all of that and there were actually no cuts in the original wiring. This was all after the plug for the wiring that comes from the front of the truck.

They didn't even tap into the reverse lights at all with the harness. So I went ahead and made a small incision in the cover. Here is what I found:

-Yellow wire is hot (blinking) when you signal left.
-Dk Green wire is hot (blinking) when you signal right.
-Lt Green is hot (blinking) when you signal left. Lt Green is dead when you signal right.
-Brown (at license plate wire) is hot when running lights on.
-All wires hot when pressing brake or hazards engaged.
-I removed the ground right behind the driver tail light, everything still works (albeit wrong) even though it is not grounded there????

This makes me think it has to be in the dash somewhere.

In reality the B/U lamps are the only culprit. They are getting power somehow when they shouldn't.

Could it be the Neutral Safety Switch? Brake Switch? Headlight switch? or my worst nightmare, inside the column?

 

[chengny]

So basically, you just got the same results on the meter as observed at the lights. Sometimes it helps to disco the suspect sections of a faulty circuit and recheck operation.

Instead of checking the various voltages at the incisions you made do this;

Pull the weatherproof plug apart and run the series of tests again. This time check voltages at the supply side of the plug.

It should be quick - all 4 feeds in the same place.

If voltages ring out normally with the business end of the harness disconnected - well at least you'll know that the problem is not in the dash cluster/steering column.

That would be the good news. The bad news would be that there is something crossed over in the section of harness that I just had spread out on my cellar floor.


But before that - and please don't get annoyed with me, but I am going to ask you once again - did you pull the lenses and inspect each socket? Specifically looking for:

1. Excessive oxidation
2. Twisted/broken posts or slots
3. That the proper lamp is installed and that it is installed correctly (this is a common cause of what you are experiencing)

If you have not done this, please do it before taking any other steps.

 

[Boone83K10]

Yes sorry, all sockets looks good. all bulbs looks good and are correct post type.

So I should check the plug, if it is good, then it has to be in the rear harness?

 

[Boone83K10]

Also tested this...

with lights off, I put it in reverse.

Reverse lights AND running lights lit up in both tail lamps.

 

[chengny]

At this point I'd forget trying to figure out what's wrong using schematics and logic. Time to go Neanderthal on it's ass!

Separate the harness at the plug, test the feeds from the cab and see what happens without all the splices, sockets and lamps connected.

If that doesn't stop the crossovers/shorts the next step is to de-energize the B/U light run from the neutral safety switch.

Here is a present -the factory wiring manual for 1983 CK 10/20/30 Light Truck series (31 pages - about 2 mb):

http://depositfiles.com/files/olmi2uowc

Cover shot below. The C/K Fleetside rear lighting dwg is on page 13:

 

[Boone83K10]

I tested the plug..

with a left signal, two posts light up blinking. From the diagram it looks like #18 and #24..so I guess that means it is somewhere from the dash to that plug. Would it be in the NSS?? When I hit the brakes, it lights them all up. Brake pedal doesn't run through NSS does it?

son of a ....

thanks but I already have that downloaded to my computer... sigh

 

[chengny]

Hey - don't sweat the small stuff (and it's all small stuff).

Do you have 2 flashers?

One in the fuse block and one in the "convenience center"?

If so switch them - matter of fact just pull the blinker flasher out of the fuse block and put in the hazard flasher (the one from the CC)

 

[chengny]

Here these dwg's should put your mind at ease.

The B/U light circuit goes nowhere near the dashboard or steering column.

Wherever the short is occuring - it is not going to be buried in either of those places.
Start with 1 and go through to 5 (follow the arrows):

 

[Boone83K10]

Yes I pulled the flasher already. I pulled both. Nothing blinks when I use the turn signal or hazard. But tails and B/U lights illuminate when I press the brake with flashers out.

 

[chengny]

The only place it comes near any other wire is in the flasher for the directionals. That 16 purple wire leads down from the directional switch in the column.

That's where was headed when I talked about pulling the flashers. The more I think about it however, don't bother. Changing it wouldn't tell you anything.

But, on the other hand, if you simply pulled it out (the directional flasher - lower RH corner of the fuse block) that would positively isolate the B/U lamp circuit from any other outside power source.

There are so many variables involved with this circuit problem - it's starting to make my head spin.

The wiring diagram for the column mounted switch that controls the directionals/hazards looks a lot like hieroglyphics or an Indian cave drawing. But it appears that there are 3 sources of power;
1. From the brake switch
2. From the directional flasher
3. From the hazards flasher

Here is the right dwg - the other one was for a van:

 

[chengny]

That's insane - it doesn't make sense. If the flasher is out (and the wiring is correctly connected and the insulation is intact) there is no way get power to those B/U lamps via the light green wire.

At least as far as the B/U's are comcerned. You have to have a cross connection to that LT GRN wire and one of the other circuits somewhere. And if the flasher is pulled out it has to be in the harness between the fuse block and the 4 prong plug.


BTW - what is the history on this problem? Did this all start to happen out of the clear blue? Or is there something being left unsaid - like an engine/transmission/rear end was changed out, major body work was done, there were other electrical issues leading up to this?

Usually when something abnormal suddenly happens in the plant - that has no known cause - I ask the junior engineers. Just tell me - don't think about it - what was the last thing you did prior to... let's say...the boiler blowing up. No matter how insignificant it seems there is often a link from the most recent change to the current diaster.


Or maybe you just picked the truck up used and it was already acting this way?

 

[Boone83K10]

BTW - what is the history on this problem? Did this all start to happen out of the clear blue? Or is there something being left unsaid - like an engine/transmission/rear end was changed out, major body work was done, there were other electrical issues leading up to this?

When I lived very close to work, I drove the truck everyday. Everything worked correctly. I have tuned the carb and put valve covers/air cleaner along with a new distributor and intake gasket. This was done back in February.

I DID put all new passenger side tank, fuel lines, fuel sender, selector switch, and dash switch. To be honest I don't see how that would effect it but I do not remember checking the lighting system after that but plenty of friends/family have been behind the truck since that and never said anything. This was done back in early May.

I bought a house and since it drinks 1/2 of a tank to go to work and back, the truck has sat a lot more. I take it to the dump once a week. I just happen to notice when I parked it this past Monday in the reflection off my Mercury Milan.

 

[Boone83K10]

Hey bit of info..

I tried to eliminate cruise a while back by removing the servo and just leaving the wiring but lost converter lockup. I put it back since it is tied into the brake switch/cruise/converter lockup.

My trans never does converter lockup now. It was intermittent and would engage if I pulled up on the brake pedal while in 4th. now it never does it.


Is this totally unrelated?