Odd issue with a 1994 GMC K1500

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AstroGoat760

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Hello,

This is my first post here, but this is my fifth GMT400 vehicle that I have owned, I have this (a 1994 GMC K1500) and another (a 1993 Chevrolet K1500), both are extended cab long beds with the 5.7L V-8 and the 4L60E transmission.

Anyhow, I started having an intermittent issue with the tail lights and blinkers on my 1994 K1500, that had the blinkers start flashing faster intermittently when the brakes and/or running lights were engaged. Now the issue is constant. I have checked the wires coming to the circuit boards on both tail lights, and there is no resistance between the brown wire (which I think is the running lights), and the black wire, which is the ground wire. I even used both my analog and digital multimeters to make sure of the resistance issue.

I am quite sure that the issue of zero resistance between ground and brown wires should not be, does anyone have any good starting points on where to look first, or should I go ahead and use my 1993 K1500 as a "template", and see what the readings are on it, and try to match?

I have a Haynes manual with a wiring diagram for my trucks somewhere, but I seem to have misplaced it. Does anyone have a good, readable wiring diagram that includes the tail lights?
 

tsr2185

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i had the same issue a few weeks ago. Swapped taillight boards and new bulbs and problem went away.
 

H2814D

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Hello,

This is my first post here, but this is my fifth GMT400 vehicle that I have owned, I have this (a 1994 GMC K1500) and another (a 1993 Chevrolet K1500), both are extended cab long beds with the 5.7L V-8 and the 4L60E transmission.

Anyhow, I started having an intermittent issue with the tail lights and blinkers on my 1994 K1500, that had the blinkers start flashing faster intermittently when the brakes and/or running lights were engaged. Now the issue is constant. I have checked the wires coming to the circuit boards on both tail lights, and there is no resistance between the brown wire (which I think is the running lights), and the black wire, which is the ground wire. I even used both my analog and digital multimeters to make sure of the resistance issue.

I am quite sure that the issue of zero resistance between ground and brown wires should not be, does anyone have any good starting points on where to look first, or should I go ahead and use my 1993 K1500 as a "template", and see what the readings are on it, and try to match?

I have a Haynes manual with a wiring diagram for my trucks somewhere, but I seem to have misplaced it. Does anyone have a good, readable wiring diagram that includes the tail lights?
Are you sure your bulbs are all good? Check them, before you start messing around with anything else.
 

GoToGuy

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A hyper fast flash is most likely a burnt out bulb, not a ground issue. No lights or dim lights = no ground or corrosion in ground point. Broken or degraded circuit boards in tail lights.
Step on brakes if both brake are on bright the problem is up forward. Turn and brake use same bulb filament. Running light is separate lower wattage.
 

AK49BWL

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A hyper fast flash is most likely a burnt out bulb, not a ground issue. No lights or dim lights = no ground or corrosion in ground point. Broken or degraded circuit boards in tail lights.
Step on brakes if both brake are on bright the problem is up forward. Turn and brake use same bulb filament. Running light is separate lower wattage.
But he's already said the bulbs are good and the issue only happens when he hit the brakes before.
 

AK49BWL

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Ah, my mistake... I might have been reading two different threads and got them confused. However, I would have to assume if he's going so far as to check the wiring, the bulbs have already been checked.... Or am I giving people too much credit here :rofl:
 

AstroGoat760

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Well, I figured out the problem with the tail lights, and it was not a ground or a bulb issue. The brown wire connection had somehow broken it's insulation at a joiner, and was intermittently contacting ground at first, then near-constantly.

I had to remove the tail-end wire harness to dissect and troubleshoot it, but I got the truck's lights working perfectly now.

Thanks everyone for the help and advice.
 
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