Can I eliminate flash from center brake light.

[48ply1stcar]

When the emergency flashers are on I get a sight flash in the center brake light.  Not noticable when checking the turn-signals.

 

I split the brake wire (circuit) to the center brake light and to the flasher/turn signal switch.  I understand having some bleed to the center brake light.

 

My question is there either a resister, or a capacitor that I can use in the brake wire to stop the bleed over.

[Merle Coggins]

A diode would block current from back feeding, but I have to wonder if there is an issue with your signal switch, or how it's wired. Although I've never tested mine to see if the 4-ways power up the brake feed. Maybe it's normal. If you put a diode into the brake feed to your signal switch that will keep it from back feeding to your center light.

 

Merle

[Ulu]

Try putting a temporary ground wire from a center lamp housing screw right to the battery ground terminal.

 

See if this makes the "ghost" flash go away.

 

This weak flash usually happens because of a poor ground.

 

Current goes up one filament and there's no good ground, so it goes backwards down the other filament, because they are both connected at the brass bulb base (which should be grounded.)

 

Because the current goes through both filaments in series, and then to a ground which is all the way back at the switch under the dash, the light flashes weakly.

[Plymouthy Adams]

Try putting a temporary ground wire from a center lamp housing screw right to the battery ground terminal.

 

See if this makes the "ghost" flash go away.

 

This weak flash usually happens because of a poor ground.

 

Current goes up one filament and there's no good ground, so it goes backwards down the other filament, because they are both connected at the brass bulb base (which should be grounded.)

 

Because the current goes through both filaments in series, and then to a ground which is all the way back at the switch under the dash, the light flashes weakly.

say what..

[Sharps40]

He said try cleaning and or adding a good ground to your center light. Bad grounds often result in weakly glowin/flashing bulbs that would otherwise be off

[Robin (UK)]

Yes.

Definitely sounds like a poor ground.

[48ply1stcar]

Center brake light has only one element.  Without having a diagram right now I trying to discribe the set-up.  Before I added the center brake light the wire from the brake switch to the input of the turn-signal switch.  The rear lights are wired like trailer lights, dual element blubs, brake and signal to the bright element and the tail-lights and license plate light are wired from the light switch. 

 

I spliced the center-brake light wire into the brake light wire before the turn signal and flasher.  I'm only getting a faint flash in the center brake light when the emergency flashers (both lights) are flashing.  Right now I assume that since there is no current in that circuit it's just bleeding to ground.

[Ulu]

Center brake light has only one element...

 

You mean one filament.

 

I totally misread the first bit though, when you said, "I split the brake wire (circuit) to the center brake light"

I thought you meant you had put a dual filament bulb in the third light.

[Ulu]

Center brake light has only one element.  Without having a diagram right now I trying to discribe the set-up.  Before I added the center brake light the wire from the brake switch to the input of the turn-signal switch.  The rear lights are wired like trailer lights, dual element blubs, brake and signal to the bright element and the tail-lights and license plate light are wired from the light switch. 

 

I spliced the center-brake light wire into the brake light wire before the turn signal and flasher.  I'm only getting a faint flash in the center brake light when the emergency flashers (both lights) are flashing.  Right now I assume that since there is no current in that circuit it's just bleeding to ground.

 

...so the center light is bright when you brake, but dim when on the 4-way flashers? And the two taillights flash OK on the 4-ways?

[Ulu]

say what..

 

I wrote: "Because the current goes through both filaments in series, and then to a ground which is all the way back at the switch under the dash, the light flashes weakly."

 

Sorry, that's wrong.

 

It doesn't ground under the dash at all. I wasn't thinking clearly when I wrote that.

 

It typically flashes weakly in these "feedback issue" problems because one tail bulb isn't grounded.

 

The juice goes through one stop filament, (on a bulb without a ground) then through its tail filament, to the tail light wire--which is hooked to nothing under the dash when the light switch is off-- but is hooked through the other tail light filament, to ground.

 

So the weak flash is because you're running 3 filaments in series on voltage adequate to run only one.

 

This is a very common problem, and I used to see it all the time when I was renting out trailers to people, 40 years ago.

Edited September 4, 2015 by Ulu

[Merle Coggins]

it does sound like the 4 way flasher signal is back feeding the brake switch wire, therefor it is powering your center brake light. If you add a diode between your splice point and your signal switch that will block the voltage from feeding back to your brake light, but will still power up your other brake lights through the signal switch. Just be sure you get the polarity right. If you put it in backwards your center light will still flash like now, and your other brake lights will not get power.

 

Merle

[48ply1stcar]

Thanks,  I'll try adding a diode this weekend.