There are 3 wires that go to the throttle, let's call them SOURCE, SENSE, and GROUND. With ground as reference: sense is at a constant +5V, SENSE controlls motor speed. Impedance from SENSE to GROUND is about 600Kohm, SENSE positive, power on. When SENSE rises above 110mV the motor control circuit energizes. Below 180mV the motor doesn't turn but it becomes much more difficult to turn it backwards or forwards. Above 180mV the motor starts turning. No matter how slowly SENSE is raised the motor starts abruptly with a slight jerk. Motor speed rises in proportion to the voltage on SENSE until it reaches 3.6V at which point the motor abruply jumps from medium to full speed.