Hi Kent, unfortunately the three position switch is only suitable for low current use
(2-3 Amps max) and you would need a switch that can handle at least 30 Amps to safely carry the full current being drawn from the battery by the motor.
Here are a couple of switch suggestions:
100Amp Battery Isolator Key SwitchAlthough these battery isolator switches are very robust, they can also be more awkward to mount on the bike due to their size.
16 AMP DPDT Rocker SwitchAlthough this is only rated as a 16 Amp switch, because it is a double pole switch, there are two sets of contacts which are each capable of carrying 16 Amps. If both pairs of contacts are wired in parallel, the 16 Amp switch should then be able to safely carry 32 Amps.
Whichever switch you decide to use, it might be better to mount it on the frame
(rather than on the handlebars) so that the thick wires carrying the current are not being subjected to continual flexing
(caused by the movement of the handlebars while steering and balancing etc.) which could eventually lead to cable failure due to metal fatigue.
Alan