Brake Light Bizarre

I took my car for a drive on Memorial Day and when I got it into the garage, I noticed that the brake lights were on, even with the ignition switch off and no one in the car.

I have a dual piston master cylinder with two electrical sensors that lead to somewhere. One, or both, must be for the brake light. When I have my wife step on the brake pedal, the brake lights will flicker, but not go out. I bled the brakes, but to no avail.

Is this a case of a failed sensor on the master cylinder?

Chuck

loose grnd wire?

yes - definitely sounds like a screwy ground.

when i was doing my wiring harness - I was shocked at what the lights did without a ground. It was using the filaments as a ground - some lights super bright - some super dim - overall really confusing.

test them out by running a separate, clean ground to the battery.

Thanks guys. I will give it a try and report back in a couple of days.

I'm betting on a bad brake light switch. It just happened to me a couple of weeks ago. I made a quick run down to Autozone and had it fixed in about 15 minutes. Easy job, just unscrew the old one, screw in the new one, hook the wire back up and you're done.
Troy

When my brake lights went south, I found I had on of hose "dual elec circuit" senders on my master cylinder. Switched the hot lead to the unused terminal and everything was up and running again. Nice to know I had a redundant system.

That was the first repair I did on my Speedster when I got it last year. A 10 dollar part. I have a spare in my extra parts bin For when it happens again.

Dave

Some master cylinders have places for two brake switches. You can use one as a hot spare. If the first one fails, just move the wire and you're back in business.

The 2 wires attached to brake light switch located on the master cylinder are as follows: One wire is 12 v positive and the other wire runs to the rear of the car and activates the brake lights. Remove either wire and the brake lights should turn off. Tough them together and the lights should activate. It makes no difference where the wires attach to the switch as it's hydraulic activated. When you step on the brake pedal and exert pressure, the switch makes contact bringing the 2 wire terminals together thus completing the circuit.