Here a little bit more with PC, it's a real pain to write with touch screen phone. My Trailtech 8500-RS switch had different colour wires than the picture I posted above. The wires of my Trailtech RS-8500 switch were: white, green, yellow and red. Though it was easy to test which is for which button. At my switch the red wire was input, the white was the output of the top button, green of middle button and the yellow of lowest button. Also I soldered the TT red wire into red wire of Rostra switch harness for 12 V input, TT white to Rostra Yellow and TT yellow to Rostra green. The top (RES/ACCEL) and lowest (SET/COAST) buttons off TT switch are now working. I also soldered the TT green button to the Rostra brown, but as wrote above, the middle button won't work as a ON-button. Like Mr Canoehead wrote, there maybe should come constant 12 V+ into brown wire for ON. There must be a little relay in the Rostra switch, pressing ON gives constant 12 V+ to brown wire (and lights the green led of the switch) and pressing OFF stops the 12 V+ from brown wire and shuts down the green led. I didn't test rode yet, but ran the self diagnostics, pressing top or lowest button lights the red testing led of the Rostra CC just like pressing RES or SET buttons of Rostra. Will test ride tonight. Two more questions: 1) When now having the middle button of the Trailtech switch spare, it would be nice to have a Cancel-function for this button, saving many brakings... The light green wire of Rostra harness is soldered into the ground side of BMW clutch switch and so would be near. Also the cancel function would be possible with the clutch safety feature? My TT middle button, green wire, gives 12 V+ when pressed, but how to use this for Cancel-function with Rostra Clutch safety wire. I don't understand from the Mad Kaws first post how the clutch switch work. When I press clutch, does it give 12 V+ for the Rostra too, or does it give ground/stop giving ground? The first one would be easiest, then I could solder the TT green to Rostra light green, but should I use a diode between the soldering point and BMWs clutch switch? The two last options, clutch switch giving/stopping ground, would need a relay? 2) If I would like to eliminate the Rostra switch completely (of course would need the think replacing leds also) could I replace the Rostra On and Off -switches for example the Trailtech 040-HBS-03 ON/OFF rocker switch. Then the red wire of the TT on/off switch solderet to Rostra red wire and the TT black wire to Rostra brown wire. So the constant 12 V+ for the Rostra brown when the TT switch is ON. Edit, test ride done, RES/ACCEl and SET/COAST working well from Tt switch. Huge improvement for ergonomics. Well worth of 18,50 £.