Tail light/brake light problem

My car has an electrical issue w/ one of my tail lights. When the lights are on, one side is much brighter than the other. Actually, the brake light is always on, on that side, wheras the other side is normal. Any thoughts?

Sounds like the brake light switch is stuck in the on position & one brake light is burned out.

Does your cruise control work?

What are you driving?

In most cars, one brake light is wired to the other one rather than both of them having separate wires to the brake light switch. Makes the wiring simpler. What you are describing can’t happen with a car wired that way. If one bulb is on for any reason, they will both be on.

But … a lot of cars use one bulb with two separate filaments for brakes and rear turn signals. It’s impossible to tell from outside which filament is lit or if both are lit. I suspect that maybe the light that is brighter and on all the time might actually have the turn signal light permanently on. The turn signals are wired separately for both sides so difficulties with one side will not automatically show up on the other.

With the engine off, turn on the emergency flashers and see if they work normally (they share a lot of wiring with the turn signals). Turn them off, turn the ignition key to on, but don’t start the car, and test the turn signals. I’m guessing that you will find that either the emergency flashers or the turn signals or both will misbehave.

I see, I guess I haven’t tested the turn signals, however the turn signals on the dash always seem to be fine. Why test w/ the engine off, any reason?
BTW, car is a '95 Ford Aspire, the car that aspires to be a real car someday!

***Why test w/ the engine off, any reason? ***

Not really. Minor safety issue. The engine doesn’t have to be on to test the lights, and leaving it off eliminates any chance of accidentally pushing the transmission into gear while climbing in and out to push buttons and view the results. I don’t trust parking brakes. They tend to be pretty feeble.

I guess it is possible that the bulb in the brighter side is installed incorrectly. There is only one way you should put in a two filament bulb, but sometimes a clueless person will force in a bulb incorrectly. I would check it.

I agree with what Wentwest says. The two filament bulb is reversed so the brake light filament is connected to the tail light circuit. This will make the running light brighter than it normally should be since it is a higher power filament.

Is he brake light on even when the headlights are off? A lot of things would be have to be wrong for one brake light to be on all the time, its not logical. It might be possible if you had a ground hunting brake light system, but I don’t know of any that exist.

Most brake lights get their 12v through the brake switch and find ground just on the other side of the bulb through the socket or through a ground wire. If the ground wire is broken or the socket is corroded, both filaments of the bulb will light whenever the headlights are turned on, but the light will go out when the brakes are pressed. It will also go out when the headlights are turned off.