Tail light action, or lack of it.

[Socopunk]

Have an aftermarket tail light. Noticed that when the rear brake is pressed there is only a very small change in brightness. Also, one filament is lit and when the switch is pressed the same filament gets slightly brighter. What does the other filament do? I have switched the two hot wires thinking I wired it wrong and when switched there is no change in brightness when the brake lever is pressed. Stock tail light works fine. What am I missing here?

Also tried the stock bulb in the aftermarket housing and same as above happens. When stock bulb is put back in stock housing, it works fine.

 

[jamesgs4]

bad contacts in the socket?

 

[Tech7]

Sounds like you got a bad ground. 3 inputs. Parking, small filament, stop, large filament, and a good constant ground. What is likely happening is that when you hit the brake, the increased amperage required makes your poor ground go away, and the current tries to ground through the other side of the bulb. Happens all the time on things like plow trucks, and trailers.

 

[littlebill31]

2 filaments means that one is brake the other is running light. Make sure it's grounded good. This might mean grounding the light housing to something. Some lights don't come with a black ground wire, so you have to make your own and attach it to the frame or other grounding wire.
There should be 2 or 3 wires from the light. Some only come with 2, which is what I have. One brake one running. Ground the light and attach one wire to your running light, then switch. Obviously the bright one is your brake light.
I bought an aftermarket light and it didn't work. Had 3 wires, but one filament. It said brake/running, but nope. If I tested the wires one would blow the fuse. Got the instructions?
Check all your connections and go from there. Hope that helps.

 

[Socopunk]

Thanks for the info guys. I know the stock light had 3 1/2 wires. What I mean is a Blue and Yellow Hot and a black ground running to the cluster under the seat. It also had a black ground that ran to a mounting bolt for the tail light housing. Just realized that is probablly what I'm missing. I will try it out when I get home later today.

 

[littlebill31]

On mine the blue is running and yellow is the brake.
A bad ground can be a pain.

 

[nj1639]

Yeah, I changed out to a Lucas style tail light with just 2 wires. Had to take the stock ground wire and remove the tab connector that attaches to the bulb socket and replace that with a washer type connector and then mount that to one of the tail light housing mounting bolts....all's well.

 

[Socopunk]

Just an update on this. Made the bolt mount for the secondary ground and it still didn't work. Took the whole light apart and found that they used the yellow wire as the ground!!! Re-wired and it works great now.