AFAIK, the "speed sensor" you refer to is the PAS sensor. There's a small bulb on the unit, and if this lights up when the system is activated, it's operational FME. If not, you need to discover whether it's the sensor or the wire at fault (might be easiest to just replace the $10 sensor and determine whether that solves the problem), then act accordingly. I'm pretty sure you'll need to remove the motor from the cycle if you need to disassemble it. Also, you might call or email Luna Cycle; they have been very helpful to me in the past.