Weird Brake light problem

[The Money Monk]

I have a 95 Chevy G10 cargo van that is giving me a perplexing minor issue with the brake light.

When the lights are off both brake lights work. When the lights are on, the driver's side brake light is alwaays on as if the brake is being depressed, but the passenger side light functions normally. WTF?

It has led to several people telling me my brake light is out when driving at night with the lights on, but its not out it's just actually always on. It is brighter than the other side but just doesn't change when the brake is depressed. What gives?


Easy fix, or a weird electric gremlin?

[Spork]

This is a WAG based on a problem my dad had a few years back...

He had the type of tail lights that had a 2 filament bulb in them.  One filament is the brake light.  One filament is the running lights.  He had a bulb burn out and replaced it with a single filament bulb.  In doing so: he crossed 2 circuits.  In his case, when he put on the brakes stuff would work (radio, some interior lights) and when he let them off, they'd lose power.  In theory, I guess a failed bulb could cross 2 circuits as well (if filament #1 broke in a way that the hanging chad crossed the 2 circuits).

Is this at all a possible scenario? 

[The Money Monk]

well they are 2-filament bulbs, but I don't know where anything would have been crossed. I replaced it with another 2-filament bulb, so not sure where a cross would have happened.

[dragoncar]

I know nothing about the particular issues, but it definitely sounds like there is a short somewhere.  There's really no other explanation for why turning on the headlights would force the brake light on.

[Spork]

It was totally a guess based on a single experience... don't let it side track you.  ;)

If you have recently replaced one of the lamps... you might try a second lamp there just in case...  If that doesn't work: My guess is likely 100% wrong.

[The Money Monk]

It was totally a guess based on a single experience... don't let it side track you.  ;)

If you have recently replaced one of the lamps... you might try a second lamp there just in case...  If that doesn't work: My guess is likely 100% wrong.

At least it gives me something to try. Thanks.

[The Money Monk]

I know nothing about the particular issues, but it definitely sounds like there is a short somewhere.  There's really no other explanation for why turning on the headlights would force the brake light on.

Yeah that's my guess, I just have no idea how to find out where it is

[Greg]

well they are 2-filament bulbs, but I don't know where anything would have been crossed. I replaced it with another 2-filament bulb, so not sure where a cross would have happened.

Try removing and reinstalling the bulb, with special attention to the little nubs on the sides of the bulb base, one is farther from the point than the other and if installed incorrectly, the circuits can get mingled.  This is for 1157 type bulbs.

[The Money Monk]

well they are 2-filament bulbs, but I don't know where anything would have been crossed. I replaced it with another 2-filament bulb, so not sure where a cross would have happened.

Try removing and reinstalling the bulb, with special attention to the little nubs on the sides of the bulb base, one is farther from the point than the other and if installed incorrectly, the circuits can get mingled.  This is for 1157 type bulbs.

These types of bulbs are actually polarized? so it matters which 'nub' is on which side?
/

[Greg]

If it's a two filament bulb, yes.  The orientation of the bulb in the socket determines which filaments in the bulb are powered by the different contacts in the socket.  One is typically brighter than the other; the bright one is brake or turn light, the dimmer one is running light.

If you study the bulb, you will see the nubs are different distances from the base tip. The socket grooves match this difference.  It should only fit one way, but the metal of the socket can be flimsy enough to allow the bulb to be installed 180º out of alignment if you're not careful or don't know.  Especially on older cars.

[The Money Monk]

If it's a two filament bulb, yes.  The orientation of the bulb in the socket determines which filaments in the bulb are powered by the different contacts in the socket.  One is typically brighter than the other; the bright one is brake or turn light, the dimmer one is running light.

If you study the bulb, you will see the nubs are different distances from the base tip. The socket grooves match this difference.  It should only fit one way, but the metal of the socket can be flimsy enough to allow the bulb to be installed 180º out of alignment if you're not careful or don't know.  Especially on older cars.

Thanks, I will check it out and see if I put it in backwards.