1997 Silverado K1500 - No brake lights or head lights

[98Z]

I do believe that my truck hates me...

For some reason, the brake lights quit working. Blown fuse, ok no problem. Replace the fuse, touch the brake pedal, blows the fuse. Spent $15 to buy a new brake light switch. That thing is a pain in the ass to change. But, that didn't fix the problem. Grrrr!

Fine, so today I tear apart ALL of the wiring from the firewall to the light bulbs in the back. There is NOTHING wrong with any of it. The tail lights work. The turn signals work. The 4 way flashers work, until I touch the brake pedal and it blows the fuse again.

It was suggested that there might be something wrong in the turn signal multi-function switch (4-way flasher button was screwy, possible short in there), so I spent the $100 to buy a new one and tore apart the steering column to replace that mess. That's a bit of work.

The column is back together. The 4-way switch works great, the turn signal switch is smoother, but I still have no brake lights and the fuse blows every time the brake pedal is touched.

Also, now I don't have headlights! Turn the key on and the daytime running lights come on. Flip the switch to turn the headlights/taillights on and I lose headlights, but the taillights and amber parking lights in the front are on.

Is there a mechanic in the house?

I'm losing my mind here!

[Schurkey]

Line up a bunch of fuses of the CORRECT AMPERAGE, or a suitable circuit breaker that can be reset.

What is the system voltage with the engine running at fast idle?

Take the brake light bulbs OUT, touch the brake pedal. Does the circuit protection still pop?

Does the truck have a trailer-light connector? How is it spliced into the vehicle wiring?

[98Z]

Originally Posted by Schurkey

Line up a bunch of fuses of the CORRECT
Take the brake light bulbs OUT, touch the brake pedal. Does the circuit protection still pop?

I completely removed the entire rear harness from the equation by unplugging it at the firewall under the brake booster. It still pops the fuse

Does the truck have a trailer-light connector? How is it spliced into the vehicle wiring?

Yes, it does. It is a plug-n-play unit. Disconnect the harness plug and put the trailer wiring plug in between.

[777stickman]

Pick-ups use a "stop lamp relay" in the underhood fuse block. Could be an issue with that.

[98Z]

Originally Posted by 777stickman

Pick-ups use a "stop lamp relay" in the underhood fuse block. Could be an issue with that.

That has been checked.
I even replaced it.

[777stickman]

With the relay removed does the fuse still blow?

[98Z]

Originally Posted by 777stickman

With the relay removed does the fuse still blow?

Yes, it does.
Thankfully, I have found a 20A circuit breaker to use instead of blowing 400 fuses while I attempt to track down this problem.

On a more positive note, I have headlights again. It would seem that something went wonky in my snowplow harness. I might need a couple new relays for that issue. I'll deal with that at another time, I just really need break lights

[98Z]

Apparently I have mis-remembered everything I did last night trying to sort out this mess.

While I've been messing around with it today, I have found that if I have the rear harness UNPLUGGED, the fuse does NOT pop when the break pedal is depressed. Also, when I have the rear harness disconnected, I do have a functioning high-mount 3rd break light. I was thinking there might have been a bad wire grounding out on that, but that doesn't seem to be the case.

So, let's recap...

My headlights are no longer an issue; that is snowplow harness related and I'll deal with that at another time.

I do NOT have fully functioning brake lights.
I tough the brake pedal and it blows the fuse.
I HAVE replaced the brake light switch.
I HAVE replaced the multi-function switch.
I have checked all bulbs in the taillights.
The boards in the taillight housings are brand new 3 months ago.

Four-way flashers work.
Turn signals work
Taillights & reverse lights work.
This leads me to believe that I do NOT have a wiring harness issue from the cab to the rear of the vehicle.

However, if I disconnect the harness at the firewall that powers the rear of the truck, the brake light fuse does NOT blow out. This leads me to believe that there is a wiring issue in the cab in the brake light circuit and I don't recall taping into any wiring for anything.

[777stickman]

Just for future reference, the rear turns, the rear hazards and the brake lights all use the same bulbs and wiring from the multi-function switch on back. The 3rd brake light is wired separately.

This harness you're disconnecting, is it a 5 wire flat connector below the brake master cylinder with wire colors BRN, PPL, YEL, DK GRN & WHT?

If so, I may have a solution to your fuse blowing short.

[98Z]

Originally Posted by 777stickman

This harness you're disconnecting, is it a 5 wire flat connector below the brake master cylinder with wire colors BRN, PPL, YEL, DK GRN & WHT?

If so, I may have a solution to your fuse blowing short.

Yes, that is the plug I've been disconnecting.

[98Z]

I have had the issue resolved.

After many hours of messing with this stupid thing, I finally just dropped it off at a shop. They located a direct short in the plastic block that gets the wiring harness through the firewall. It has been repaired and everything it back to normal now.

I thank everyone for their attempted assistance.

[98Z]

After countless hours of fighting and attempting to track this down, I finally just dropped it off at a shop that an acquaintance of mine owns. After a couple of hours of them searching, they found a direct short in the 2 piece plastic block that passes the wiring through the firewall. That has been repaired and everything is back to normal.

Thanks to all for the assistance.