Question About Tail/Brake Light

[marcopolo]

If I recall correctly, the tail/brake light bulb on my 1150R had a dual filament, i.e., one filament for the tail light, and a second which came on when the brakes were applied.

 

On my R12RT, each of the two tail/brake light bulbs has have a single filament. How do they work; what makes the bulb brighter when the brakes are applied if there's only one filament? Is the bulb operating at reduced intensity when it's just performing the tail light function, then increasing to 100% intensity when the brakes are applied (like some Daytime Running Lights on cars)?

 

I just bought a spare bulb,and noticed the single filament. The parts guy said it was the correct PN, and I confirmed this on the online parts fiche at MAX BMW's site. I then took the tail light assembly apart to eyeball the two bulbs to make sure. They do indeed have single filaments.

[Albert]

Hey Mark,

I'm not positive about this but I believe the Canbus controls the brake light. The computer senses the brakes being applied and supplies the correct voltage/current to the bulb depending on the desired brightness. At least I think I heard that somewhere.

[99Roadster]

Manual lists it as a P21W (21 watts). Looks like an 1156 single-filament.

 

More than likely it uses half wattage as the tail light and full wattage as the brake light.

 

This is comparable to my Honda's daytime running lights using the high-beams at a lower wattage during the day and full wattage when used as high-beams.

 

Oh, and my 1100R also uses a single dual-filament bulb.

[BeemerEric]

The brake lights on the can-bus bikes use pulse-width modulation, I will show you here...this is what the voltage looks like with the brake light OFF:

 

[BeemerEric]

This is what it looks like with the break light on:

The voltage does not change...it is just pulsed when you are not applying the breaks.

[BeemerEric]

I used this info for a freind who is an electronics engineer...he designed a small electronic circuit for me to control some custom brake lights I installed.

[marcopolo]

I used this info for a freind who is an electronics engineer...he designed a small electronic circuit for me to control some custom brake lights I installed.

 

Wow, you're way ahead of me on that stuff. I was feeling proud just being able to take the light assembly apart and unscrew the bulb (testing my on-the-road repair procedures, limited as they are. That's not to say I've attempted the headlight bulb though ).

[GoGo Gadget]

I used this info for a freind who is an electronics engineer...he designed a small electronic circuit for me to control some custom brake lights I installed.

 

Is this something that can be easily replicated without an EE degree? I installed a Whelen LED light as an aux brake light. It stays bright as a running light. It gets brighter still when the brakes are applied, but it is too bright and distracting in running light mode.

[sundaeman]

You might try putting a resistor in the running light circuit to drop the voltage going to the Whelen.