brake light problem

[Boog]

Hi guys. I have a problem with my daughters 97 GMC.
All stock truck.

Just this week the brake lights don't work right.
When you start pushing down on the pedal the lights come on but go off instantly and stay off until the pedal is released and they come back on and go off just as fast. It's like there is only one spot in the switch where it makes good contact. I replaced that switch with a new one and have the same symptoms. I can hold the pedal at the spot where the lights come on and they stay on ok but push the pedal just a tic further and they go off. All bulbs, fuses and relays are good. All lights are bright.
Any ideas?

[ChevyTech]

It sounds like is could have burned contacts in the relay for the high visibility brake light.

[FMBL]

I had a similar problem with my 89. It was the brake switch that is on the steering colum.

[Boog]

As mentioned I have already replaced the switch with a new one from the parts store and it does the same thing.
I switched relays with 4 other ones and no help.
I hear from a couple of local mechs they have been through this same thing numerous times and it was the switch. So I picked up a new one from the dealer and I'll try it today.
The one that came off the truck was mexican made. The first one I bought at parts house is Taiwan made. The one I just bought from the dealer is mexican made. I sure wish that little pain in the ash was easier to get to!
And that irritating little retainer clip, well, I've lost blood each time I've had one off.
What's the chance it's not the brake switch but the torque converter lockup or cruise control causing this? The brake switch is wired to both of these as the cancelling tool.
Or how about the turn signal switch?

[bwood]

Originally Posted by Boog

What's the chance it's not the brake switch but the torque converter lockup or cruise control causing this?

I believe the brake switch affects these two, not the other way around. The brakes turn off the TCC and cruise.

[ChevyTech]

And that irritating little retainer clip, well, I've lost blood each time I've had one off.

They are a pain in the a$$. I think of the man hours wasted across the country fighting with that damn clip.

As mentioned I have already replaced the switch with a new one from the parts store and it does the same thing.

Was the part in an unopened sealed package? Could someone have cleaned there old switch up and returned it to the store which then sold it to you.

[Boog]

No sealed packages, just in boxes. No doubt they are new parts though. I did buy another new switch from the dealer and just put it on to no avail. Same thing.
I've pulled all fuses, replaced the brake lamp relay with other known good ones, disconnected the tail lamp harness at the rear of the truck, pulled cruise control fuse, unplugged the abs controll box. Still does the same thing.
Since the brake lights go through the turn sig switch is that maybe the next suspect?
It is strange how it is pressure sensitive.

[clinebarger]

Originally Posted by Boog

No sealed packages, just in boxes. No doubt they are new parts though. I did buy another new switch from the dealer and just put it on to no avail. Same thing.
I've pulled all fuses, replaced the brake lamp relay with other known good ones, disconnected the tail lamp harness at the rear of the truck, pulled cruise control fuse, unplugged the abs controll box. Still does the same thing.
Since the brake lights go through the turn sig switch is that maybe the next suspect?
It is strange how it is pressure sensitive.

Have you checked for broken wires and bad connections? The switch moves with the brake pedal so it chould be losing contact. Press the pedal & wiggle the wires, have someone tell you if the lights flicker on & off.

[Boog]

Actually I have. While there is no extra length to the wires they don't seem to be binding when I push the pedal. I have given thought to pulling the instrument panel out to get a better look at the wiring. Maybe I can do that tomorrow night. Thanks.

[bwood]

Originally Posted by Boog

I have given thought to pulling the instrument panel out to get a better look at the wiring.

Removing the cluster will only reveal that the cluster sits in a plastic "bucket" molded into the dash. All you can see is the plug in for the cluster and not much else. There are some small holes that maybe you can peer through, but thats it.

[Boog]

Well that bites doesn't it.....I'm not the contortionist I used to be so I'll go back under there and see what I can find. At least we have a spare truck for the daughter to drive. Thanks.

[TwoFiftyShifter]

Had the same problem at my truck, lihts only came on the first couple inches of pedal travel. I couldnt figure it out, but it turned out there is a connector near the steering column, and it was just the way it was hanging. I stuck it up on the steering column with RTV, lights work fine now. Not sure if I helped at all, it was kindof a quick fix.

[Boog]

Glad to hear it was so simple 250. I hope mine is too.

[ChevyTech]

If you think it could be the turn signal switch, take a test light and see where it has power and where it does not.

If I remember correctly the wire from the brake switch to the turn signal switch is white on these vehicles, but I can’t picture in mind the brake circuit for the trucks with the third brake lamp, so I can’t sure or more specific.

The early 1990 trucks sometimes had problems with the brake lamp input wire to the turn signal switch right at the connector to the turn signal switch on the column.

[buffle]

Could it be the circuit boards in the tail lights? My taillights would work sometimes on the drivers side, but the blinker would do about 4 blinks and then no taillights at all. New replacement circuit board cured it.......just my 2 cents.

[Boog]

Originally Posted by TwoFiftyShifter

Had the same problem at my truck, lihts only came on the first couple inches of pedal travel. I couldnt figure it out, but it turned out there is a connector near the steering column, and it was just the way it was hanging. I stuck it up on the steering column with RTV, lights work fine now. Not sure if I helped at all, it was kindof a quick fix.

Well now 250 I just came in from messing with it and found if I pushed back on the switch itself the lights came on and stayed on ok. When I push the brake pedal I see the wires move with the brake switch and they go off. So it looks like there is a connection issue much like the one you had.
Right now I have the switch tilted upward and it's working fine. It's not right but it's working. The wires aren't pulled as much this way. I have narrowed it down to this.
Now tell me how you managed to get in there to see the connector and stick it in place would ya? Remove the steering column? Geez!

[TwoFiftyShifter]

No I didn't remove the column, I simply realized that moving that connecter up towards the column was magically making the lights work, so I glued it to the column with black RTV. That was in May and they are still working. I can take a picture of exactly what mine looks like now if you'd like.

[Boog]

I got ya. If it's not raining I'll get out there again tonight and see what I can come up with. Thanks.

[Boog]

Good news. I found the problem. The wire harness from the brake pedal switch has broken wires in it. I saw how the lights worked when I moved the wires back and forth so it had to be a bad connection or bare spot or something like that. I dropped the tubular support under the steering column and a large wire harness connection to gain access the the short harness from the brake pedal switch. My local Oreillys located a new short harness and should have it tomorrow. I'm glad it wasn't the turn signal switch, $190!
I'll snap a pic of the broken harness tomorrow.

[TwoFiftyShifter]

Good to hear you actually took the time to correctly fix the problem. I feel like I went a different route. HA!

[Boog]

It's back together and working. The replacement harness didn't work out. It was only a pigtail and the wrong one at that. So I pulled the wires out of the connector and spliced them back together. I made sure there was plenty of slack for movement. Daughter is back in it and happy.

[bwood]

Awsome