It sounds to me as if the basic speed switch has failed. It might be worth removing the control panel (the screws are underneath).
Switch off first. Remove the positive battery lead if you have any doubts, dont short anything!
Don"t unplug any wires before carefully labelling and photographing it all in detail so that you don't go wrong when reassembling.
Take a good look at the underside of the 4 -8 mph switch, has a wire come loose? Follow the wire, has anything become detached? If not it MAY be the switch, these are often on offer on eBay
Answers & Comments
It sounds to me as if the basic speed switch has failed. It might be worth removing the control panel (the screws are underneath).
Switch off first. Remove the positive battery lead if you have any doubts, dont short anything!
Don"t unplug any wires before carefully labelling and photographing it all in detail so that you don't go wrong when reassembling.
Take a good look at the underside of the 4 -8 mph switch, has a wire come loose? Follow the wire, has anything become detached? If not it MAY be the switch, these are often on offer on eBay