ben2go
OBS Enthusiast
True I guess but that wouldn't stop power from getting to the fuse. The fuse protects the switch at the pedal.
No brake lights. Brake light circuit diagram needed.
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someotherguy
I'm Awesome
Thing to always keep in mind is there are two VERY different steering column setups in the GMT400's. Your truck is what - a 96 or 97? Nothing at all like OP's 89. There's no multifunction switch in his, like in yours. Almost all the functions in the 88-94 are individual switches, not a combined unit.
Richard
ben2go
OBS Enthusiast
Good point. I didn't think about that. The changes to the column happened around '94/'95 if I'm not mistaken.
slovcan
I'm Awesome
Yeah, sorry, mine is a 1997. So, the main brake light wiring doesn't pass through the multi-function switch pre '94/'95? Or, is that a maybe?
someotherguy
I'm Awesome
There is no multifunction switch pre-'95, that's what I'm saying.
There is a separate turn signal switch, and presumably the brake light signal does go through it as the signal would need to interrupt it since GMT400's combine brake/turn functions. These switches aren't known for going bad, whereas the 95-up multifunction is a bit notorious (generally for the hazard button breaking off.) Not impossible that it's bad, just not highly probable.
Richard
The 94 and earlier models. (Easier to remember. ) Turn signal is still the same circuit. The brake light filiment and turn filiment are the same. The 95 and onward just have added functions to the turn signal switch unit. But the basic circuit for brake and turn is the same.
just wondering if you ever found out wat it was
ben2go
OBS Enthusiast
I never figured out the no power at the fuse block ordeal 100%. There could be a circuit breaker somewhere that I didn't find. I don't think it would be factory though. My son and I are 3rd owners of the truck so who knows what the POs did.
When I got back on it, I pulled two fuses, the signal fuse and the brake fuse. I checked continuity on the fuses instead of just looking at them. I've had them go bad in my other vehicles and look fine. Both fuses checked out. I probed the fuse block and had power. Before, I had no power. I put the fuses back in and power was restored. I think corrosion in the fuse block was why I had no power at the fuses. I should mention that both tail lights were out of the truck when I did this. They could have been shorting something out causing the no power at the fuse block problem, I don't know.
I moved on and checked the tail lights. All I had was park/driving lights. A few months ago my son and I replaced the tail lights and circuit boards. The boards are Dorman brand and came highly recommended. I can't recommend them. Let me explain. When we installed the boards, they worked perfectly. I didn't question the new boards. I popped the bulbs in, installed them in the light housings, and installed them in the truck. The worked perfectly at first.
I pulled the bulbs and probed the boards for power. The board contacts for the bulbs are getting power but none of the bulbs were working. I eyed the board contacts while installing the bulbs and they didn't line up. They were off to the side and the little wire the bulb uses to press against the contacts had bent just enough to not make contact. I think the heat cycling of the bulbs cause the wires to deform enough, after getting bent, to cause them to loose contact. I straightened the wires on the bulb bases. I bent the board contacts over to match the bulb contacts and bent them out to put more pressure on the contacts. Over the past week, we've had no problems and check the tail lights daily. The boards were made in a way to prevent the contacts from aligning with the little wires on the bulb bases. When I say I bent the board contacts, I really bent them. They look deformed now but it's what I had to do at the time to get them to work.
I'm looking at converting the old OE light boards over to the old bayonet style connectors and run 1156 and 1157 bulbs. I can do it and keep the factory wiring harness connector between the bulb and body harness. Everything will work and look just like factory after the boards and tail lights are reinstalled. If I do it, I'll do a write up and post it here. I may make a video about it.
Cadillac Bob
Slammin original 4x4 Cadillac doors!
It could be the that black size of a deck of playing cards connector/actuator thing that is up behind your brake pedal they sometimes get temperamental so once in a while I’ll have to lay on my back reach up in there under the dash/brake pedal an just in snap it an it works fine again then resnap it back after it doesn’t like that position anymore lol. Or possibly have you pressed your E brake just a bit an pulled the tab to unlock it? But you really didn’t you have to push it in as your going to really use it then pull tab to unlock E brake off and then your lights will work I figured that out after needing the headlights off but keep fog lights on at night to go on a Xmas lights trail on a farm. Maybe this could solve the problem but I didn’t read everyone’s replies lol good luck!
My 94 does have a multi function switch.
I dont know when they changed that but all kinds of odd things happened mid year in 94.
And a 95 is really odd.
You can pull the brake light switch and take it apart if you are carefull about.
The contacts break and they weld themselves together.
And the metal hinged contact point that the rod goes through wears out and the rod starts ovaling out the plastic.
At the same time, the spring inside the switch gets weak.
Thus the contact welding from slow release and the intermittant brake light flashing.
And it may react differently when that switch is warm than it does when its cold
It may arc together and short for a bit and weld itself together and only release when it cools.
eventually, enough crap builds up that one or maybe all of those contacts are making intermittant contact or even welding themselves together
The other thing to think about is on a 4l60e. Torque converter lockup runs through the brake light switch circuit.
You could quite easily have a brake switch failure and a multi funtion switch failure at the same time.
At least on a 94 you can.
If you decide to replace the brake light switch.
It is a bit of a ******* to do.
By the spare clip from Dormann.
That clip tends to go flying away and a 2 buck spare might save the day
I dont know when they changed that but all kinds of odd things happened mid year in 94.
And a 95 is really odd.
You can pull the brake light switch and take it apart if you are carefull about.
The contacts break and they weld themselves together.
And the metal hinged contact point that the rod goes through wears out and the rod starts ovaling out the plastic.
At the same time, the spring inside the switch gets weak.
Thus the contact welding from slow release and the intermittant brake light flashing.
And it may react differently when that switch is warm than it does when its cold
It may arc together and short for a bit and weld itself together and only release when it cools.
eventually, enough crap builds up that one or maybe all of those contacts are making intermittant contact or even welding themselves together
The other thing to think about is on a 4l60e. Torque converter lockup runs through the brake light switch circuit.
You could quite easily have a brake switch failure and a multi funtion switch failure at the same time.
At least on a 94 you can.
If you decide to replace the brake light switch.
It is a bit of a ******* to do.
By the spare clip from Dormann.
That clip tends to go flying away and a 2 buck spare might save the day
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