Yet another brake light question

[snakeeyes]

A while back, I posted a query concerning my lack of brake lights. I was promptly given the appropriate part # for ERA brake light switches. I only replaced one as my local parts store only had one in stock. The brake lights seemed to work fine afterwards, although I confess I only tried them with the car's lights (i.e., head- and taillights) switched "off".

I then went to the Texas Cobra Club's annual meet. On the way home from that, running at night with the car's lights on, I was told that I only had one brake light working. I took a quick look this past weekend and here are the symptoms: Both brake lights work when the car's lights are not on, UNLESS the left-hand turn signal is switched on, in which case only the passenger-side brake light works. When the car's lights are turned on, only the passenger-side light works, irrespective of whether the left turn signal is on.

Bob P., do you think this is related to my only having replaced one switch, or is it something else i.e. faulty wiring elsewhere, etc.? I could spend some time crawling around under the car with a circuit tester, but with a newborn at home it sure is a lot easier to type on the keyboard.

Thanks for any help anyone can lend.

Bob

[RACER X #99]

Bob,
Check the ground connection for the lights. a loose or missing ground will cause all kinds of goofy things to happen.

Cranky

[Tommy]

I'm assuming a lot about your car, but here goes. Each tail light assembly probably has two wires coming from the rear of the light bulb part of the assembly. There is likely a third wire from one of the bolts holding the assembly in place to a nearby ground. First, make sure each assembly is in fact grounded. Of the two wires going to the back of the bulb, one goes to a bright filament and the other goes to a dimmer filament. When you step on the brakes, only the bright filaments should illuminate. If one side is bright and the other side is dimmer, that may be part of the problem. When you turn on a turn signal, the bright filament on that side should flash on and off. If your turn signal circuit is wired correctly, that will happen whether or not you are stepping on the brakes.

If both assemblies are grounded, and both bright filaments light when you step on the brake, and both dim filaments light when you turn on the parking lights, then your tail lights are likely wired correctly. If this is the case, the problem is likely under the dash where the lights are wired to the various switches. Do a little more troubleshooting and tell us what you find out.

[snakeeyes]

Thanks for the input, guys. Next time my baby daughter allows (i.e., some time around July), I'll head out to the garage and check it out. Cranky, I haven't been grounded since I was four and stuck a fork in a light socket, but hopefully the same isn't true for my Cobra...

Tommy, that sounds like an interesting split window you've got there. How about some pics in the photo gallery?

Bob

[Bob Putnam]

A bad ground gets my vote too.

A less likely cause would be a bad bulb contact plate - damaged or reversed in the socket.