The picture in near the bottom of the Ebay listing seems pretty straight forward despite the confusing number of wires.
For the throttle, first distinguish between the connector for the throttle and the one for the 3 speed switch, since the descriptions by the Chinese are lacking. The throttle will have a single wire at +5V, a ground, and typically in the middle is the sense wire. The 3-speed will show a 5V differential across 2 of the combinations with the 3rd wire.
Reverse is simple. It's just 2 wires that you wire a switch across. Completing the circuit is reverse (usually speed limited to something like 30% and open circuit is forward.