None of the 3 brake lights illuminate when the brake pedal is depressed. After checking the two tail lamp bulbs I assumed the problem to be in the stop light switch. Replaced the switch today with no change. Turn signals, reverse lights, 4-ways, ...all other lighting functions properly.

I'm hoping someone can help me out with the wiring pinout for the stop light switch, an FSM wiring diagram or even just help me to better understand the basic brake light wiring theory for this car. Does closing the switch contacts provide ground or power, or both, to the lights? Is there a fuse I'm not aware of?

I'm paranoid that a rodent may have decided to rewire some things on this car while it sat awaiting an upper ball joint and a t-belt for 4 months. I've had electrical problems with the blower motor for the HVAC and I also had to replace the cam sensor last month. Ah, the joys of rural living.

 

I can't speak for your car specifically, but:

Typically, the brake light switch has voltage going to it and it will complete the circuit to allow that voltage to continue to the brake lights. The ground for the brake lights should be provided at a spot close to the brake lights (IOW: in the trunk area).

The other lights work properly because they are on different circuits. Now, I'm not familiar with your particular car but if it is wired like most cars:

You'll need to check the fuses first to eliminate that as the problem. Then, you should check that there is voltage to the switch (ensuring that the circuit from the fuse to the switch is intact). Then you should check to see that voltage goes through the switch, and gets to the brake lights, when the switch is depressed.

It is possible that your car uses a 'body controller' to take car of all the lighting, etc... If that is the case, then each switch simply completes a circuit to the body controller and it sends the outputs as necessary. Perhaps someone else can tell you specifically what system your car uses. I've been out of the auto repair business for years, so I just gave you the basic layout of typical and newer systems.

-Good luck, Ken

 

Thanks for the reply and well wishes. I was assuming that the switch sent power and the lights had a local ground, so that's assuring. I'll never understand why any of these newer cars ever needed a "body controller".

Still holding out hope that someone out there has a factory service manual and can give me the pinout and power take out circuit for that switch.

 

there should be a fuse or relay under the hood in power distribution box . you should have power at brake switch connector in cavity 6 for brake lights, #5 is output to brake lights, # 2 is the ground ,# 3 is cruise control power supply,#4 is cruise output, #1 is brake switch signal, the brake lights don't go through body control module.

 

Thanks BillS, that's what I needed. It makes sense now from my continuity check on the switch today.

Underhood fuse is good, already checked that. Also verified the grounding is good with a meter. I traced wires and the grounding point appears to be located under the carpet just below the striker for the trunk lid. Then I broke the selector switch on my el-cheapo DMM right after that, or I'd have probed the switch for power next.

This is stumping me. How can I have a good fuse, good ground, good switch and still not have brake lights? The only options left are no power supply to the fuse or a broken wire with no short, right?

 

Yes. A broken wire causes an OPEN circuit as opposed to a SHORT circuit. Likely places for an open circuit is anywhere the wiring gets flexed. IOW: it's common for broken wires to happen near the door hinges (power window, power door locks, etc...) and near the hinges on hatchbacks (rear window defroster, third brake light, etc...).

If someone has added something (aftermarket stereo, amplifier, anti-aircraft missile barrage, etc...) start checking around there. Most of these wounds are self-inflicted.

If you have power to the #6 connector (as per the info that Bill gave) that means that your wiring from the battery to the fuse and the fuse to the switch is good. If you jump #6 to #5 you should have power to the brake lamps. If not, there is an open circuit between the switch and the bulbs. If you recently replaced the switch, don't bother trying to jump out the pins, just depress the brake pedal and check to see that you now have voltage at #5 connector pin / cavity. If that works, that means that your switch is working properly. Just get a short piece of wood and place it between the drivers seat and brake pedal. Then move the seat forward far enough for the wood to depress the brake pedal. That will hold down the pedal while you go looking around for the broken wire. Of course, when you are working near the brake pedal, you should note the color(s) of the wire going to pin/cavity #5. That will tell you what wire to look out for while you go tracing down your open circuit.

-Ken

 

I understand the difference between open and short.
Car is 100% stock.

Jerry-rigged broken meter shows no voltage at pin 6 on the brake switch connector. Tried jumping pins 5 and 6 to verify the meter is correct and confirmed no lights.

Also, all I have to do to ensure the switch is closed is pull it out of the hole it mounts to the pedal assembly with and leave it plugged in. The sprung plunger moves out of the switch when the pedal is depressed, or when you remove it from being sandwiched in the pedal assembly.

So it looks like I have a break under hood or under dash. Oh joy.

 

try unhooking battery for 10 minutes ,then rehook and start let car run for 5 minutes and see if that does anything