I have a custom built E-bike and it was working just fine up till yesterday. It got caught in some heavy rain, and from that point on it's been giving me problems. At first when I turned on my "Go fast Switch" the motor would make this sound, and I had not even touched the throttle, and even when I tried the throttle the motor would not engage. I then started to pedal, and after switching the battery on and off a few times, I finally got the throttle to engage the motor, but it wasn't acting right. It was like it was stuck in the middle of my low and medium on my "Go fast Switch". I wasn't getting the torque I normally get and it wasn't reaching it's normal top speed. Switching it from low, Med, High had no effect.

I bring it home, let everything dry and then tried out the motor again. It spins but it sounds very rough, but it's speed would increase when I set my switch from low, med, high. So that's fine. I let it sit some more, and tried it again later on. Nothing. It's like I don't even have the throttle on. If I switch the battery on and off several times, I can sometimes get the motor to engage for a half a second, then nothing.

I've checked the voltage on all my wires, and everything checks out. I have voltage going to the throttle, but when I twist it. The voltage does not change. I opened up the throttle to have a look inside and I can't figure out why it's not working.. I think it's my throttle, as I can't see what else it would be. Something is shorting out somewhere, and my lead suspect is the throttle.

Suggestions ?

I had the same problem after going through a few heavy rain storms.. it was the control/display unit..just too much moisture has seeped in.. swapped it out for a new one at the place i bought the bike from.. works great now.
Got caught in a bad downpour last night and took shelter, also wrapped plastic bag around the control unit.. Avoid getting it really soaked.

You think it's my "Go fast Switch" ? This is what I call the "Go fast Switch"

I manged to open up the King Meter/current bypass switch and there was no water or any indications of water getting in or any signs of damage. The board looks perfectly normal to me.

I think it was the throttle. Everything works now that it's dried out for a few days.