if you manuall turn the rc servo to the high position, with the TPS connected and turn the ignition on, does the servo move to the low position, suppose this would indicate the servo does work. I can only imagine if the servo does work, and the cables allow it to do then perhaps the TPS if faulty?? Without looking at the wiring diagram i can only imagine its a simple two way switch and perhaps you could simulate the TPS operating by shorting out the correct pins on the TPS connector to see if it operates the servo or prob better, check the resistances with the throttle open and closed at the TPS end of the lead.

I'll be working on my bike tomorrow night and have the carbs off so could do some comparrison measurements for you to check against.

cheers
Brendan