85euro928

While at Hershey someone noticed that my LED brake lights on my euro have a slight glow without the pedal being pushed and without the lights on. So before I waste an entire weekend troubleshooting just to get nowhere I figured I'd ask to see if anyone else has had this problem before as a search of the forums revealed nothing. I thought that it might be the Lamp Check Unit but yesterday I disabled pin 2 which made the warning light go off but the brake light glow is still there. Looking through the WD's I imagine it does have something to do with the Lamp Check Unit as the alternative cause appears to be voltage leaking into the circuit from another source which seems unlikely. Any help would be appreciated.
Thanks

j.kenzie@sbcglobal.net

Hi Thom,
Same happened tome. Also my cruise control and remote start malfunctioned due to thinking the brakes were on. The easiest solution is to put an incandescent light back into your third brake light. I'm sure you can install a resistor of appropriate size somewhere, but this solved the problem for me.
Good luck,
Dave

85euro928

Dave,
Thank you, if only I had a third brake light (it is in the planning stages though)
I didn't want to have to add a resistor as that partially defeats one of the reasons for switching to LED's but if that's what it takes...

davek9

Bypass the Lamp Controller and also wire the Lamp controllers "input" for stop lamps directly from the brake peddle switch, that will eliminate the warning computer under the dead peddle.

The illumination is coming from the bulb sensing, to see if a bulb is out

EDIT: this sounds like a lot but only takes less that 1/2 hr and is fully reversible if you don't cut any wires (and you do not have to), just unplug them and replace w/jumpers.

Alan

No it isn't - the bulb check unit doesn't work that way - it only monitors filament status when the lamps are activated - using the activation to detect voltage drops over a series resistance.

As above - this actually comes from the Cruise Control which uses the low resistance stop lamp filaments to monitor brake status. A resistive pull up on the brake lines allows it to detect when the brakes aren't on - it sees low voltage on the brake line due to the low filament resistance & when the brakes are activated this goes high. The resistor value is high enough to that it won't illuminate incandescent bulbs but it is low enough to make an LED glow. This also usually causes the cruise control to malfunction.

You may have enough spurious warnings you will want to eliminate the bulb warning circuit - but it will be for a different reason.

Alan

Want to be

I'd begin checking your ground wires.

Mrmerlin

Phil I suggest to read what Alan wrote about how the bulb check system works.

Thom doesnt have a grounding issue

j.kenzie@sbcglobal.net

Hi Thom.
One way to fix your problem would be to add an incandescent third brake light in parallel with your existing lights. It avoid resistors, and adds safety.
Good luck,
Dave

davek9

OK, than that's why you need to directly wire it from the Peddle switch to stop the "glow".

Alan

There is a possible solution to this issue that doesn't make the brake LED's less efficient. Use an SPDT (Bosch type) relay with the coil connected to the brake line (86) and ground (85) - so it activates only when the brakes are on. Connect the common switch terminal (30) to the brake line and the normally closed connection (87a) to a resistor to ground. The resistor will only be connected when the brakes are off so will dissipate very little power (only the cruise control current). I'd suggest a resistor value of maybe 6 ohms.

Alan

davek9

Thank you Alan, great solution/suggestion, will give that one a try

Dave

85euro928

Yea I think I'm just gonna live with the glow
Thank you.