After finishing, but before you go on a test ride, check all of the cables and connections. Many times I’ve solved people’s computer and printer problems by simply asking them to make sure the thing is plugged in.
I had everything wired together on my bike and flipped the switch. Nothing. Immediately, I assumed I had a bad controller or motor, but once I settled down I started tracing wiring. I unplugged the (very firm) throttle connector, and plugged it in again. Bingo. It ran like a charm.
If your system doesn’t work, give everything a once-over and double-check every connection. Possibilities are sometimes a bad controller; rarely a bad motor; and maybe a defective throttle. The throttle is easy to test. Most kits come with two—a twist grip and a thumb lever—so it’s just a matter of switching throttles and trying again. But 90% of the time, the problem will be a connection.