RT-P L.E.D Brake/Tail light

[Bradl K]

Does anyone have experience with the BMW LED brake/tail light? I received one as a gift and really want to use it, but the instructions say'Not for Cam-bus applications'. It is my understanding that the police RTs are Cam-bus also. So why would this not work on my RT (an 07). The dealer that sold it to them told them it would work on my bike. I called them and told them what the instructions said and they said they would refund the money if I did not want it. I really would like to use it, but don't want to harm the bike!

Brad K

[Woodie]

Newer model BMWs (all types) have CAN-BUS. (1150 & newer, IIRC)

 

This is a code word, to mean that the electrical output of each circuit is monitored, and can be shut off if there's too much current running through it. It's also used to scare people away from adding electrical things to their bike.

 

So:

Use an existing CAN-BUS circuit (parking lights?) to turn on a relay, that connects a direct line from the battery to the device that you want to power. Bypasses the existing circuits almost entirely, and let's you do what you want.

 

For brake lights, I'm not sure. I suspect the LEDs would draw LESS than the stock, which might cause the CAN-BUS to report a bulb problem. You could use the brake-light circuit as your relay trigger.

[Bradl K]

The instructions have the unit connecting to the battery for power,and uses splices in the brake/tail light wiring in the bulb housing to trigger the brake light. I've read that devices that connect to the battery don't seem to bother the Cam-bus system.

BTW, my instructions do say CAM-BUS, is this an error in spelling? This is a BMW part, however the packaging says 'Made in USA'.

Brad K

[BailyD]

I run my radar directly from the battery with no problems. I leave it on all day long, 2007 R1200 RTP. No error messages. BMW has a specific plug for our radar, but it powers down a minute after you turn the bike off. I can't run stationary radar with the bike idling or the ignition power on.

 

 

 

[Pictou]

I have always seen it referred to as can-bus so it may be spelling error.

 

It sounds like the light you have is for the older bikes. The can bus stuff was introduced with the R1200 series. I suspect if BMW is saying not for canbus systems then it likely won't work. I do have sort of a vague recollection that there was a BMW led for the 1150 and older bikes.

 

Some with a better knowledge of the electrics than I do can correct this but I believe I have read that the R1200 tail light is modulated by raising and lowering the voltage. I don't think they aren't dual filament bulbs. The lower power setting is the running lights and the high power is the stop light. Not sure what this would do but if your light is triggered to come on when it sees power then it might be all the time as there is power all the time. All this is just speculation on my part.

 

The instructions have the unit connecting to the battery for power,and uses splices in the brake/tail light wiring in the bulb housing to trigger the brake light. I've read that devices that connect to the battery don't seem to bother the Cam-bus system.

BTW, my instructions do say CAM-BUS, is this an error in spelling? This is a BMW part, however the packaging says 'Made in USA'.

Brad K

[jskene]

There is a good reason why your brake light says it is not compatible with the R1200RT.

 

On the BMW R1200RT and K1200GT, BMW does not use the normal dual-filament rear bulbs, but rather two single-filament brake light bulbs. There is no tail light filament.

 

The ZFE control module, which controls the motorcycle's lights, sends pulsed, 12-volt power to the brake light filament, even when the brake is off. What this means is that the voltage on the brake light filament is rapidly switched between 0 volts and 12 volts. It spends more time at 0 volts than at 12 volts, so the filament burns only as bright as a tail light, quite a bit dimmer than a brake light.

 

When the brakes are applied, the ZFE lamp controller increases the duty cycle to 100% so the voltage stays at 12 volts continuously. This lights the brake filament up to full brightness.

 

Adding an auxiliary tail/brake light system to these bikes can be quite tricky, as there is no tail light wire, but only a brake light wire. The auxiliary brake light cannot get power from the tail light wire as there isn't one, and it cannot get a stable source of power from the brake light wire, as it is rapidly fluctuating between 0 and 12 volts whenever the brakes are off.

 

This is why the instructions on your light say it is not compatible with the RT.

 

The reason that the BMW LED is not compatible with the RT/GT is not because these bikes use the CAN Bus, but is because they use single-filament brake light bulbs.

 

Other late model BMW models that use normal dual-filament bulbs, such as the R1200GS, also cause trouble for some aftermarket lights. In addition to sending normal power to the tail light filament, the ZFE sends pulsed power to the brake light filament. You can see this if you remove the red plastic tail light shell and observe the tail light bulb. You will see that both filaments are lit up, even with the brake off.

 

BMW uses this system for two reasons. The tail light on most BMWs is notoriously dim, and so by lighting up an additional filament, they get a brighter tail light without having to add a second bulb. On the GS and some other models, the tail light section is quite small, so there is no space for a second bulb anyway.

 

The second reason is to add redundancy to this critical component of your motorcycle. If your tail light filament goes out at night, you become essentially invisible to traffic behind you, especially if you are wearing dark, non-reflective clothing.

 

Another feature, which many BMW owners are not aware of is that on some models, if the ZFE senses that the tail light filament has failed, it sends pulsed power to the brake light filament, lighting it up as a redundant tail light. Very neat feature!

 

However, the first time you're likely to find out about this (unless you're reading this article) is when your tail light fails and your aftermarket brake lights go crazy.

 

So, if you're planning to add an auxiliary or modulated brake light, check with the manufacturer to ensure that it is fully compatible with BMW's new brake light circuitry.

 

 

 

(Incidentally, the acronym for the bus is CAN BUS, which stands for Controller Area Network Bus.)

[Ken H.]

I almost hate to post this, because it will only add to your confusion, but with some electrical knowledge it is quite possible to convert any CAN-BUS equipped bike to all LED or add supplemental LED lights. Such as brake, tail, etc. I converted our CAN-BUS R1200GS to 100% LED (except headlamps of course) long ago, including with brake light modulation, with no issues. And I have added similar to other CA-BUS GS's and RT's.

 

I don’t have a chance to write a complete tutorial now, but in short the ZFE module monitors current levels of the lighting. As long a proper loading is maintained to create the correct current load, no errors will created.

 

[jskene]

The current drain caused by LEDs is a separate, albeit important, topic.

 

It won't cause a problem when you add auxiliary LEDs to your brake light, as Brad K wants to do. LEDs take very little additional current compared to the existing tail/brake light bulb and so will not cause a bulb-out fault code.

 

It's only when you replace an incandescent bulb with LEDs that you have to consider this. An LED draws much less current and so will usually trip the ZFE's current monitoring circuit, triggering a bulb-out fault code. Adding a resistor in parallel with the LEDs will fool the ZFE into thinking that the bulb filament is still there drawing current.