94 Z71 Brake Lights

[georgewe4]

I figured I would give this a shot since its midnight and I can't work on it tonight. I was informed today at church that the brake lights on my 94 Z71 are not working. I was hooking up a trailer that we are going to pull with the truck in a parade Monday when I found this out. We messed with it at church for a while before I brought it home and checked out a few things. The switch is good. There are two normally closed contacts and one normally open contact they are working properly.
The third brake light is working. The other two arent. The bulbs are good. I have no power to the brake lights at the sockets. I have no power to the wiring going to the sockets (black and brown wire) I unplugged the wiring harness that goes to the trailer wire harness plug, and still nothing. The fuses are good in the fuse panel. When I hit the brake pedal I hear a relay click under the hood. I have not checked that out any further. I am wondering if the brake light wiring runs to the anti lock module on the master cylinder? Or where it goes from the back of the truck. Where is the next point of orgin I can check for power. I tried to find a wiring diagram on the web but I can't. Anyone have any ideas where to go from here?
Thanks.

[turbofish38]

Its the taillamp socket boards. I sell them by the truckload. Every GM truck built between 1988 and 2000 will need them sooner or later. GM part numbers are LH-16511565 RH-16511566. You can also get them from AutoZone and NAPA. The copper printed circuits in them corrode over time.

[kh440]

ditto: the circuit boards are notorious problem children.

[1987BuickGN]

I agree on the circuit boards, but if that isnt it, these are some things to look for as well: Reason I say this is because BOTH sides arent working now.....

IF you have the trailer wiring kit that plugs into the trucks wiring harness, check and make sure that is tight and secure. Those "T"s are not very forgiving.

Obviously check fuses and bulbs.

Ive had a 94 and a 97. Neither had circuit board issues, but had to replace the switch on the pedal assembly in both. Im aware of ALOT that do have the taillamp circuit board issues though.

Good luck!

[Waco84GN]

I have heard of the combination switch on the left side going bad and causing symptoms similar to the ones you are having. I work for autozone and deliver parts to quite a few shops. I have learned that usually when the third brake light is still functioning correctly, but the two lower brake lights are not working that the combination cruise/ turnsignal/wiper switch may be bad. I also bought a 2001 chevy blazer and in the glove compartment was the paperwork where the combo switch was replaced under warranty due to similar symptoms. The upper kight workig, but the other brake lights not working.

Just my .02

Jerry Berger

[fullahotair]

If they are the circuit boards for the tailights, don't skimp on those cheap boards you can get from salvage yards. I bought the cheaper ones twice over two years and they don't last and give you nothing but problems. They work for a while but quickly corrode. Since then i have purchased the more expensive GM pieces and haven't had a problem since (2 years) with no issues.

[georgewe4]

Hey guys thanks for the input. I knowmy brake switch is good. It has two normally open contacts and one normally closed contact. It is working properly. I even snapped it apart and cleaned the contacts. I triet takind the trailer harness out of circuit and that didn't work. I may try that again though and make sure my contacts are good. I have continuity from the plug of the circuit board to the bulb socket, so I "think" my boards are alright. Turn signal switch??? Im wondering what that would have to do with my brake lights... I know I have no 12 volts at the brake light plug where it goes into the circuit board. I will check further.
George

[SloGN]

does the turn signals work? also check to make sure that the hazzard light fuse is good also. if the turn signals don't work and the fuse is good the combo switch is bad.



those trucks don't have idependent turn signals so in the turn siganl switch it makes the brake lights burn and the say left turn light flash when turning left.

The brake lights and turn signals use the same bulb filament. the other filament is used for the parking lights only. 3157 light bulb it does this on both bulbs in the circuit.

[georgewe4]

Wow. I know its been a while, but I am just now getting time to check this thing out further. I am getting ready to put the cap on the bed of the truck for winter so my third brake light will be hidden.
I do have turn signals. The front and rear work. I just dont have any brake lights in my rear tail lamps. Hazzard fuse? I will check that.
Combo switch still? You think?
I know the brake light and the turn signal share the same filament in the bulb.
Im getting power to the buld obviously because the turn signals blink the bulbs.

[SloGN]

actually the turn signals and the brake use diffrent bulbs. on the board

you need to check to make sure the circuits are not burnt on the tail light circuit board. also check the brake switch/ and or adjustment.


last time i remember there was three bulbs in there rear tail lamp board

you have running lights,brake/turn and reverse lights i may be wrong but i think the brake and turn works sepreatly. been a while since i had my 94

[georgewe4]

They have three bulbs. The top being a single filament bulb for lighting when the lights are on. The middle is a dual filament bulb one for lighting when the lights are on and the other is the signal/brake lights. the bottom being the back up lights. So with the middle being a dual filament bulb, the one filament is working with the lights being on as it should on both driver and passenger.
The larger brighter filament in the same bulb is my turn signal/ brake light. Both sides work with the turn signal, but neither work with the brake lights. Just my third brake light operates. There has been some mention about the turn signal switch in the steering column.
I'm lost on this one and I hate being lost on something like this.
Sorry if I spelled filament wrong.