Side markers turn on when pressing brakes

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OldBlueDually

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I didn't find anything on this--I apologize if it's nothing new to you guys!

This is for my 76 GMC 1 ton.

I see my side markers glow dim, and kind of strobe a bit (dim to somewhat bright) when I press the brakes.

So, I put it in park, held brake and messed with light switch (out and in quickly) and nothing changed.

When I held the brakes (lights still dim) and turned on the light switch they were bright.

I swear I've gotten all grounds cleaned/properly secured, and fixed bad wires--did I miss something?


Secondary to above: fuel Guage doesn't work, but selector switch does!!! Sooooo I just randomly stop to top it off!!

Any suggestions/advice/comments are so welcome---my brain hurts after the few years of work and tracing wiring on this thing!!
 

PrairieDrifter

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It sounds like an issue between the hazard system and the marker lights. Someone should be able to get you the correct wiring diagram.

Proper operation, when these trucks have the hazards on and you press the brake pedal, the front markers stay solid when the brake lights are on. Im not sure with headlights on, i know they still stop flashing but I don't know if it stops on the brighter output or the normal output.
 

rusted nuts

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I didn't find anything on this--I apologize if it's nothing new to you guys!

This is for my 76 GMC 1 ton.

I see my side markers glow dim, and kind of strobe a bit (dim to somewhat bright) when I press the brakes.

So, I put it in park, held brake and messed with light switch (out and in quickly) and nothing changed.

When I held the brakes (lights still dim) and turned on the light switch they were bright.

I swear I've gotten all grounds cleaned/properly secured, and fixed bad wires--did I miss something?


Secondary to above: fuel Guage doesn't work, but selector switch does!!! Sooooo I just randomly stop to top it off!!

Any suggestions/advice/comments are so welcome---my brain hurts after the few years of work and tracing wiring on this thing!!
I swear You don't have all the grounds fixed.
 

mibars

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Side markers, you mean the front ones? Front ones use a trick of being grounded via turn signals, so that they go off when the indicator lamp turns on. By any chance you have any LED bulbs that may mess up resistances?
Rear should be just connected to park lamps.
 

OldBlueDually

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@rusted nuts I was swearing a little bit too!!! :Big Laugh: I am sure you are right though...sick of wiring.

@mibars Oh man, I am sorry I should have explained better! The side front markers on my dually fenders are the ones I saw in my mirror doing that--I did not have anyone around to check out the other lights for me. For the record, no I do not have any LED bulbs in anything--these are the stock style bulbs in everything around the truck.

Sorry guys about not explaining the exact markers---front dually fender orange ones. I need to have someone stand around the truck as I press the brakes and see what other ones do this.

This is what sucks about a low truck--it's a lot of work to jack it all up and crawl around for wiring issues.
 

v30

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Check the brake light bulbs for filament sag, could be getting feedback that way.
 

Matt69olds

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Push and pull the hazard switch knob several times, see if that does anything for your market light issue. Sometimes that “fixes” quirky tail/brake/ marker light operation.


If you are positive all the bulbs are correct, the sockets are clean and making good contact, and all the grounds are good, try a new turn signal switch. Just plug it in, don’t install it until you are sure it solves your issue.

There are about a dozen different switches that open and close depending on turn signal switch position, any one can cause funny light operation. It’s kinda amazing they don’t give more problems than they do.
 

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