Resolved: F800GS Brake Modulator not modulating

dacrazyrn · January 23, 2010, 04:38:16 AM

Hooking up the Brake modulator to the 09 BMW F800GS. Back panel off, found the gray and black striped wire and brown ground. I have a Centech fuse box in the tail, so I sent the ground and the power straight to that, then cut the gray/black stripe and connected the yellow coming in and pink out to the LED light plug. Turned on the bike...rear light modulating about every second. Hit the brake and works like it is suppose to, BUT after that it will not modulate again....even after several minutes. Only the straight brake light comes on.
Do I need to connect the ground to the incoming brown wire of the brake light? Only thing I can think of. Don't want to cut into it unless I have to.
Thanks

Fluke · January 23, 2010, 07:09:10 AM

Hi

Sorry your having a few teething problems.

I think I know whats going on here.

The modulated brake light should kick in when you apply the brake.... and this is the only time it will modulate. (it shouldn't modulate the second you turn on ignition)

I think you have the yellow wire from the podmod connected to normal rear light feed rather than the switched brake feed... (this explains the modulation when you turn on key and normal operation of the brake, as your putting the rear light through the modulator rather than the brake)

The pink must then goto the brake wire going into your rear LED cluster...

Let me know if above makes sense... I can draw a little diagram or research your bikes wiring further to give you colours etc if it would help

Regards

dacrazyrn · January 23, 2010, 08:09:10 AM

Shots of the tail of 09 F800GS. Standing at rear of bike facing forward. The only 2 wires going into the LED brake light.
I cut the gray and the yellow went to the left of the arrow and the pink to the right (down to the plug).

Fluke · January 23, 2010, 10:07:59 AM

Hi

Thanks for the shots....

For the F800 is the brake / rear light LED cluster only powered by those two wires ? ....or are those two wires 'just' the brake.

I'll give John a shout who makes the Modulators for us... but I'm thinking if there are only two wires for both brake and rear light that might be the problem and the modulator won't be compatible.

I'll drop him a email now.

Cheers

dacrazyrn · January 23, 2010, 10:34:19 AM

Only two I have found going into it. The rear brake light does run at ~30% running light and full on with the brake on. In the picture there are 2 other sets of wires and plugs...I am guessing that is the L and R turn signals. nothing else going into the LED brake light

zeuter · January 23, 2010, 12:37:40 PM

Hi Dan,

I agree with everything you've said, but we need to know if there is a seperate TAIL light. If not, and the cluster serves as both Tail and Brake lights, ie reduced power for Tail and full power for brakes. It could be a new fangled BMW thing and we'll need to dig deeper. If Tracy has a test meter, a voltage reading on the BrakeMod Yellow, brake on and brake off would help tremendously. Any voltage reading with the brakes off would suggest a combined Brake/Tail system. I suspect that if the one led cluster does the job of both brake and tail light, then with the brakes off, the yellow will be getting a pulsed 12v feed (reduced power for tail light) which will give the symptoms described.

I'll post a copy of this on the forum.

Regards, John

Fluke · January 23, 2010, 03:53:38 PM

I don't think the Brake mod is going to work with your F800 without some major modifications and in depth research into how BMW create the rear light / brake switchover (probably with modulation)

This more complex setup means that the brake mod is (as John says) always being activated.

I would be more than happy to research further, or you can return the unit for a full refund.

Regards

edit: I've updated the brake light mod page to ensure this doesnt happen again

dacrazyrn · January 23, 2010, 07:53:21 PM

Got it to work using what you have in this diagram. Figured if it has power going to it constantly, should be able to use as the red wire power source. Doesn't have a 5 second "timeout" though. Flashes every time...fine by me.

Fluke · January 24, 2010, 09:15:42 AM

Thats fantastic, so glad you got it working.... I'll make a note for this for other BMW riders

Thanks for all your patience...

Regards

zeuter · January 24, 2010, 10:58:38 AM

Hi Tracy,

Well, now I'm really confused! (easy to do). If the Red and Yellow are getting a constant voltage with the brakes OFF, then this setup shouldn't work unless this voltage is quite low (around 2 volts) or it is a pulsed 12v supply.

Have you still got a Tail light? Assuming you have, and the voltage is low, then the initial power surge on applying the brakes must be resetting the microprocessor and allowing modulation. Have you tested it with the engine running at 1400rpm or higher? This will raise the voltage slightly and the unit may stop modulating although the brake light should come on as normal. I think it is important you check this as the unit was not designed to work this way.

If it is a 12v pulsed supply, then I am quite happy with the set up, as the processor (which runs at 4MHz) simply resets with every pulse.

A voltage reading on Red/Yellow would be great if you have the means.

Regards, John

dacrazyrn · January 24, 2010, 12:32:25 PM

Tail light is still working with only power on and works as "advertised" (modulating) with pressing the brake on and off repeatedly.. Will start her up tomorrow and see about the rest you wrote about. It is staying 35 degrees F and below here and it is trapped by snow, so can't actually ride it, but can run her up in N and see. try to get the multimeter to give me some readings. Old and piece of @#$%...so will see. :D

dacrazyrn · January 24, 2010, 09:51:34 PM

Turned it on today. Working fine. Started it up and it idles about 1400rpm. Running light and brake light working fine as is the modulating. Revved it up to 4000rpm in N and checked all again and it is fine.
;D ;D

zeuter · January 25, 2010, 09:15:55 AM

Ok Tracy, as long as you are happy! I just need to get to the bottom of that output signal with the brakes off. Dan may know someone in the UK with an F800GS, or a friendly BMW mechanic. I've trawled the web for info to no avail, I think the 09 is just too new for anyone to have uploaded a wiring diagram.

Thanks for all your efforts, it's much appreciated.

Best regards, John