Electronics question. Third brake light.

I am having issues with the third brake light on my roadster. Check it out here http://www.jalopyjournal.com/forum/showthread.php?t=685236

I am running a pentastar turn signal module. https://signaldynamics.com/index.ph...page=flypage.tpl&product_id=34&category_id=73

This module looks after the brake and turn signals, front and rear. It enables the use of brake lights as turn signals and is self canceling. The module takes a signal from the brake light switch and then sends signals to the brake lights etc.

The third brake light is NOT included in this module circuit but also takes its feed from the brake light switch on the pedal box.
The problem I am experiencing is that the third brake light (LED) has a dim glow when the key is on and no brakes or headlights on. When the brakes are applied the third brake light comes on full strength with the brakes lights.

My thoughts are. Do I need to put a small resister between feed and earth on the third brake which would be overcome when the brakes are applied?

Anyone got any ideas?

 

The problem is that the third brake light is LED...

The module is 'leaking' a small amount of voltage/current into the brake light circuit. So yes, installing a resistor 'across' the light will cure the problem. But make sure the resistor is rated high enough in watts that it can take the heat if the brake lights are on for any time (I'd go 25W minimum). Also mount it where the heat won't cause problems....

 

Below the chart on modules, asterisk mentions indicators glowing. Sounds like you are hooked into that circuit, possibly. What did Signal Dynamics say when you called them?

 

As stated above a resister of the correct value should most likely solve the problem but you could also use a relay to accomplish the same thing without heat or current concerns. My question to the manufacture would be is it normal for the module to be constantly supplying low voltage on that circuit?

 

On my hot rod builds with a third brake light I thought of a rather simple fix:

Use TWO brake light switches - one for the conventional brake lights and a second switch independent of the rest of the turn / hazard / brake light mish-mosh solely for the third light. Works for me.

 

Thanks Steve.

Cheers, I haven't called them......yet! I didn't think it would be too major to sort. Thanks for your help.

The relay idea may work. Thanks.

It may be a little late in the build to incorporate this, but certainly a good fix.
Thanks.

 

Use one brake light switch to control multiple relays.

 

i used a diode in my exciter wire to my alternator, it stopped it feeding back.

 

I had trouble in another car I built. The electric fan spinning would feed back after the key was off and the engine would slowly die, long enough to get out of the car! A Diode fixed that one!
The fan in this car has a relay so no trouble this time.

 

Put a simple SB540 diode (band toward Pentastar brake input, other end to brake switch). Hook the 3rd brake LED to the brake switch. Diode will prevent leakage current from Pentastar from lighting the 3rd brake LED. No high wattage resistors needed. Just remember that the diode must be rated at 5 amps forward current, so if you go to RADIATION SHACK for one, make sure you mention this.

 

Thanks for that. Another stop to make on Monday when I am in town.
Cheers.