I have a co-worker with a 2000 Hyundai Elantra with a perplexing problem.
Whenever she turns on her headlights, the brake lights & tail lights come on together. If the headlights are off, the brake lights work as they should.
At first, we thought it was the brake light switch (we didn’t install the new brake light switch, yet), but we discovered that the brake lights were lit (I pulled of the fixtured from the housing and discovered that both filaments were lit).
Is there a short circuit somewhere, or is the headlight switch bad? My co-worker was pulled over by the police and given a “fix-it” warning (otherwise, she’ll get a ticket unless hte problem is repaired).
Thank you.
Mark B Handler
I suspect two problems. First, if the brake light and rear tail light use the same composite bulb, replace both left and right. Second look for a bad ground somewhere in the circuit.
The next thing I would suspect would be a problem in a computer controller, which could be a real pain and expensive to fix.
Good Luck
I really wonder about that police ticket. I don’t see a safety problem, unless you mean that the brake and tail lights come on anytime the headlamps are on and not, as I had assumed, that they work normally when the headlamps are off, but that when the headlamps are on the parking lights & brake lights come on when the brake is depressed. In either case see above.
It could be as simple as a bad fuse. Check the fuses first. The way some car lights work the tail lights and brake lights will ground back through the headlights when the tail light fuse is blown, and you get odd things like you describe. Replace whichever fuse controls the brake and tail lights, even if it “looks” good. If that doesn’t fix it, get an electrical specialist to look at it.
No, not the headlight switch. Concentrate on the rear assemblies and the bulbs themselves. Sometimes double-filament bulbs manage to have both contacts fuse together, creating a situation such as yours.
Pull the bulbs and inspect. Then use your voltmeter or test lamp to check each socket terminal for +12v when correctly switched. You should locate the problem this way, either in the sockets or bulbs.
There is a open ground in the tail light circuit. The brake lights are coming on because the tail light circuit is back feeding thru the brake lights to get to ground.
Check the ground wires for the tail lights.
If the filaments are crossed in the lights as SteveF stated you may be able to find it using your blinker system. If tunning on one side of the blinkers makes the running lights on both sides turn on then that is the side you need to repair.