Most of the time when the motor runs constantly it is due to a defective speed controller. However, on occasion, it may also be caused by a defective throttle or a short circuit in the throttle cable.
To test whether the problem is with the throttle or the speed controller, disconnect the throttle from the speed controller and turn the power switch on. If during this test the motor stops running then the throttle is defective. And if the motor still runs continuously then the speed controller is defective.
Thank you! I'll check that out.
You are welcome.
I bought a Razor MX500 in a garage sale and replaced the batteries. When I plug in the charger and press the switch to "On", the back wheel spins without the throttle being turned. I rechecked all connections and everything seems to be connected correctly. The only wires I even messed with were the battery connections when I removed them from the old batteries. I don't know if this problem existed before I changed the batteries because it was completely dead when I got it from the garage sale.