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Electrical gremlin help

pronstar

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On my 99 Suburban, a weird thing happened last night.

Torque converter wouldn’t lock on the highway, then a few minutes later all exterior lights go dark, no headlights at all.

So I pull off the freeway, lights turn back on...get back on the highway and the torque converter is locking.

I have to think these are related...but how?
A short somewhere?

Tranny is a fresh rebuild, hasn’t done anything weird at all up to this point.

Truck generally runs like a champ.


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pronstar

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I totally forgot to mention..it did the “no lights” dealio one other time, for about 15 seconds, before I had the tranny rebuilt.

It was as I was driving down my street, low speeds so no idea if the tranny was effected or not.

They all went out, then quickly just came back on.



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rivermobster

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This is a tough one...

You could stare at a wiring diagram to try and see what connector both of those circuits share, but I've heard some Crazy ass stories over the years...

The TC final control is always the brake light switch. Which sometimes Has to have a ground Through the brake like bulbs. (This is why I hate GM, they do the stupidest shit like this ever!)

So you might wanna check your brake light switch and bulbs to see if that fixes the TC.

Now how this relates to the dash lights is beyond me. Its possible they are not related?

The dash lights usually quit with a bad headlight switch. Wiggle it around and see what happens.

What trans does this thing have in it?
 

pronstar

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This is a tough one...

You could stare at a wiring diagram to try and see what connector both of those circuits share, but I've heard some Crazy ass stories over the years...

The TC final control is always the brake light switch. Which sometimes Has to have a ground Through the brake like bulbs. (This is why I hate GM, they do the stupidest shit like this ever!)

So you might wanna check your brake light switch and bulbs to see if that fixes the TC.

Now how this relates to the dash lights is beyond me. Its possible they are not related?

The dash lights usually quit with a bad headlight switch. Wiggle it around and see what happens.

What trans does this thing have in it?
Dash lights worked, just the exterior lights (headlights) went out.

4L60E
Shop that built it is very reputable.


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Riverbottom

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Does the cruse control work ? If it is having problems also, I would change the brake light switch. I have had a couple go bad over the years on my G.M. trucks.
 

MillerTime

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Check the rt (passenger ) side of the firewall just below the wiper cowl. There should be a plastic cover with grounds underneath and maybe some relays.....can't remember for sure, been a few years since i worked on one that old.
Id take all the grounds loose and put dielectric grease on and install. Or at least start there.
Could be the hd lamp switch too and the tranny issue is seperate...dunno.
 

pronstar

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Does the cruse control work ? If it is having problems also, I would change the brake light switch. I have had a couple go bad over the years on my G.M. trucks.
The cruise control did not work when this was happening. That was actually my first clue, then noticed the no-lockup, then the lights went out.

Cruise control worked fine once the lights came back on.

Does seem to point to brake light switch, but doesn’t explain the headlights going dark...?


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JUSTWANNARACE

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Had something similar on a 98-99 3500 dually.(tranny did nothing weird but) the lights every once in awhile would need a rest for a few(quit working then come back on) it was a short in the highbeam switch in the blinker arm.
 

rivermobster

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Dash lights worked, just the exterior lights (headlights) went out.

4L60E
Shop that built it is very reputable.


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For some reason my feeble mind read interior. Doh!

Wiggle stuff around while the car is sitting still. See if you can get any gremlins to pop up!
 

monkeyswrench

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I had a 99 or 2000 Tahoe come through with a similar weird issue. Park light and auto headlamp related. Traced grounds from GM...dumbass design in main engine harness, tagging rear of both heads...loom opened and all. After some time and wiggle checking...the harness bulkhead connectors into bottom of distribution box were found to be slightly worn at junction. Problems I had were not related to each other in the loom, but at the plug end. Find someone who can print out an Alldata wiring and junction diagram for you. May allow you to see if problems share a ground or a plug.
 
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