Brake light stuck on

[mikeant]

Help please. My friend has an HP2 and the brake light is always on. This problem appeared just recently after I had fitted a Touratech double headlight unit - but not immediately - it developed sometime later on a ride. Interesting the other HP2 on the same ride without a headlamp conversion developed the same fault except that is more intermittent. So I disconnected the brake light switches. Light is still on. I examined the bulb - normal as both filaments are working separately. The rear brake light switch is closed circuit with the brake off and goes open circuit with the brake depressed. I could not get the probes on the front switch reliably enough to tell you what is happening there. I guess that this has a Body control computer as the GS and all the wiring diagram will tell me is that the brake light and the switches are wired back to the black box. I am a bit stumped on this one. Any suggestions?

 

[Mr K]

Hand guard?

 

[mikeant]

Yes that would cause it but when the light stays on when both brake light switches are disconnected? No, we can eliminate that. My first thought was a dodgy switch so I disconnected them by parting the plugs and sockets. Disappointingly that did not cure the problem. The rear brake light switch goes open circuit when you press the brake. In a conventionally wired bike it would be the other way round but even so I am a bit surprised. The brake light switches are likely hardwired back to the Body control computer (if it is like my 1200GS). Some how the signal to turn on the brakelight is being given by the computer. On the 1200GS the indicator circuits work by the handlebar levers grounding the line from the computer. I would have thought that the brake light would be the same. I need a look at a wiring diagram, anyone got sight of one?

 

[NI Phil]

I had the same problem with my GSA - turned out to be caused by corrosion on the rear light - I had it replaced. Thread Here

Hope this helps

 

[mikeant]

Thanks for that. I read the thread. Ok, will examine it more carefully although I did have it apart last night when I checked the bulb out. I did not notice any corrosion. We don't get much rain in this part of the world and I doubt if this bike ever got wet. - unless someone pressure washed it of course.....

 

[GSMarc]

I had the same.

Check the little part in copper under the brake pedal, it switch off the light when you release the pedal.
Mine was broken and then too short to be in contact with the bolt's head ( was no more pushing on the switch).

I unlarged the head of the bolt with a roundel and a nut and now all is OK

 

[mikeant]

Ok I fixed it thanks to some advice from a German forum - you Brits are a useless lot! Seriously though. It turned out to be maladjustment of the front brake light switch. The first point to note is that unlike the 1200GS, the system on the HP2 works back to front. The switches are closed when the brakes are off and open when you play with the levers. Under the switch of the front brake you will see a 2mm allen socket screw. Loosen this and play about with the positioning of the switch which can now slide in and out of its slot. There will be some position where the brake light is off with the lever released. Tighten up the allen screw to lock the switch in this position. Job done! I felt so good after fixing this! The solution is logical but not logical if you see what I mean. Instinctively I disconnected both switches to isolate them as a problem, then checked the bulb etc. But if as here the switches have to open to tell the computer to turn on the brake light you do not isolate the problem, you merely turn on the light. This age of digital electronics requires a new mindset to us old lags used to more conventional electrics.

 

[Spout]

That's exactly how I fixed mine.

Presumed you'd already covered that before you started delving into the complicated electronics bit.

 

[mikeant]

Yes I got to thinking after I discovered that the ohm meter showed me that I had a closed circuit with the rear brake lever up and open circuit when I pressed the pedal. The microswitch is almost impossible to see but I could access the springy blade thingy. Over night the grey cells told me that by disconnecting the switches at their connectors I had indeed isolated them from the computer but that the computer's connections were now looking at an open circuit - which if what I measured at the rear brake switch was correct - would tell it to turn on the brakelight. Logically the problem was at the front switch. So then a thread on a German website suggested the 2mm allen screw and after some fiddling the job was done. I know it sounds crazy opening a normally closed switch to turn something on but that is what they have done here.