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Discussion Starter · #1 ·
Hello all, I have been racking my head over a simple brake light problem. Driving home the other day realized that my brake lights no longer worked (friendly driver informed).

Got home and had my son run through the normal checks; running lights/turn signals/brake depress and confirmed that they were in fact not working. So without schematics I began to check the circuit.
fuses - check
tail lights - check (ohmed out)
and loose wiring- all good

I attempted to reach under the dash to check the brake switch and found a 6 pin connector that I possibly could "jump out"
here is the plug unplugged from the switch. I would like to jump out the wires to see if the issue lies with the switch or further down the line. I have line voltage on the orange wire only.
Musical instrument Automotive tire Material property Automotive wheel system Bumper

I was able to find this scrolling the web but the wires described are somewhat dissimilar to the pic above. I have no idea which wire runs to the rear of the truck, and am unsure if there is not (another switch other than this) any help would be appreciated. Anyone familiar with a chevy electrical braking light system out there?
White Font Line Material property Parallel




Thanks


Don
 

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I don't have any experience with with the 5500 trucks; but colours are probably the same.
The orange should be 12v from the fuse (a quick test would be to pull the brake fuse, see if 12v disappears).
The switch operating should pass 12v to the white wire.
This white wire exists only if there are additional brake fuses.
The white takes 12v to a fuse for the rear right and left brake lights.
The white also take 12v to a fuse for the high center brake light (the 5500 trucks may not have this light).
The wire going to the rear sides brake lights is light blue.
If you only have one fuse, the light blue wire may go all the way to the switch and there may not be a white.
Hope that isn't too confusing.

However, check the simple first. You say you tested the brake bulbs, remember there are 2 filaments in those bulbs, one is brake and one is tail light.

And, it is possible that you have 2 burnt out brake lights .

You may also have a broken wire, or damaged connector, under the truck
 

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On my 88 the switch wore out it’d it is similar to mine there is an auto adjust or arm that sets the actuation point try to move that manually with your fingers and check to see if you can get it to actuate also both lights out could be a ground but if the run and back lights are ok then hand is good
 

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Discussion Starter · #6 ·
I don't have any experience with with the 5500 trucks; but colours are probably the same.
The orange should be 12v from the fuse (a quick test would be to pull the brake fuse, see if 12v disappears).
The switch operating should pass 12v to the white wire.
This white wire exists only if there are additional brake fuses.
The white takes 12v to a fuse for the rear right and left brake lights.
The white also take 12v to a fuse for the high center brake light (the 5500 trucks may not have this light).
The wire going to the rear sides brake lights is light blue.
If you only have one fuse, the light blue wire may go all the way to the switch and there may not be a white.
Hope that isn't too confusing.

However, check the simple first. You say you tested the brake bulbs, remember there are 2 filaments in those bulbs, one is brake and one is tail light.

And, it is possible that you have 2 burnt out brake lights .

You may also have a broken wire, or damaged connector, under the truck

I also have no experience with this truck in particular ............ But I did (use a jumper wire from the orange to the white as you suggested) and found that the brakes did not illuminate.

Perhaps you are right that the white wire is fused (between the switch and the light(s)... I will have to probe and try to find where the fuse is on this model.

I will note that when the brake pedal is depressed it does actuate the electric assist braking system that is found on these larger model truck series.

The lights located at the rear of the truck are LED and the wires that lead to this light are as you described (Brake and turn on the same circuit) both lights do blink when turn signal actuated- however
the brake when applied do not send power to the lights out back. However, based on what you said i can move on from the switch and try to find/trace the white wire and see if your were right that it travels to a bus fuse somewhere...

Thank you for your help and, no it wasn't to confusing at all (y)

Regards
Don
 

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Don, if the brake and the signals share the same wires and the same bulbs, the problem is not under the truck, or at the rear.
When they share the same bulbs, the brake circuit is wired into the signal flasher circuit, in other words, 12v, wire, fuse, wire, brake light switch, wire, flasher, shared wire to the rear and to the lights.
Not saying the flasher is bad, but it is a place to look.
 

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Discussion Starter · #8 ·
I fixed the brake light issue yesterday. it was unconventional how I did it but sometimes; one must cheat......

Having spent the better part of a day (without schematics) tracing wires
I can assure that there are plenty of safety pre-built into the stop lamp harness.
tracing backwards from the 6 pin switch I found the source of power (Orange leads directly to a fuse (hot always)
Forwards from the switch (white to yet another fuse located on second fuse block under dash)
This Second fuse actuates a (Relay that closes the stop lamp circuit) which will send line voltage through to the 2 separate fuses that feed (each dedicated light at the rear LEFT/RIGHT bulbs)
these fuses are located within the same fuse block as the second fuse

THE RELAY - there is a Orange FEED (30) -->- Magenta (86) that goes straight shot to FEED power to two independent light circuits which light the bulbs at the Rear.

I have no idea where the orange feed wire to the relay went "the bundle of wires were the size of my fist" However This is were the issue resided". So - I did find a constant HOT within that
same fuse block that was fused (the optional TRUCK BOX interior light circuit) Yep, I pulled line voltage From yet another fuse to FEED that relay on pin 30.

Mashed the brake and voila! The Relay closed and the brake lights lit.... Took another 45 min to clean and button up the cab as if I wasn't there.

I own this truck and recommend that whoever might be having issues like I had- Get a SCHEMATIC! I was in a pinch and have to make a choice that wasn't correct but worked. IF anyone knows were
this orange wire feed to the (BRAKE RELAY) comes from.... I am all ears!

Thanks

Don
 

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Don, the orange on 30 would be the load supply, I would have to say it's going to a fuse, a fuse that is blown.
However, nothing wrong with providing a different fused supply, as long as there is no longer a reason for fuses to blow.
If there is still a ground short on the load side of the relay, the "loaner" circuit fuse will blow. No big deal if it's not an important circuit.
I guess what I'm saying is don't let a brake light short blow a fuse that might power the trucks ignition, or other necessary circuit.
 
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