Sounds like a bad speed control

 

Turns out I had the switch wires reversed. I fixed that and it is no longer blowing fuses, but the red light on the throttle says "Low" and there is NO response to a throttle twist even though the batteries read 12.8V, 13.0V, and 13.1V.

If I plug it into the charger, the green fully charged indicator light comes on on the charger.

With the switch "On," I have 39V going to the controller and 1.2V coming out of the controller to the motor. When I turn the throttle, I get 1.3V.

I would think it's the controller, but the fact that the red "Low" light is on on the throttle makes me suspect battery/ies.

I hope I didn't ruin something by reversing those switch wires, but it seems the fuse that popped immediately when I flipped the switch to "On" would have prevented damage...

 

More then likely your controller is fried the fuse is just there to prevent the bike from catching on fire or the battery bank it's not intended to prevent damage from wiring things backwards or wrong voltages you can get controller kits dirt cheap on eBay and Amazon

Even when the batteries are bad they will run for 30 to 45 seconds then slowly wind down to nothing.

 

MrKitty,
In addition to the control module, do you think the batteries are also bad since they read 12.8V, 13.0V, and 13.1V and the red light on the throttle reads "Low"?

 

More then likely those trash SLA China batteries onley last about 2 years and that's onley if you store them individually on battery tenders for the winter. They also come activated it happens every spring people end up with a last year model bike because they got it on clearance then the batterys only last half the summer