Hi Roo,
Why do you need a 100A switch when the Magic Pie only draws around 30A under maximum load?
Check out
this post for details of a double pole switch that can be used with the Magic Pie.
As the switch is only operated when the motor is not running there is unlikely to be enough current to induce much of an arc across the contacts. Fitting a precharge switch as described in the above linked post will eliminate the arcing that occurs every time the connection is made and will ensure the switch contacts last a long time.
The voltmeter can be wired into either the
thumb throttle or the
horn/cruise switch. There is a "Battery +" and "Battery -" connection inside both units so it might be wise to use the horn/cruise button unit as there are no large internal moving parts to rub against the additional wires you will be inserting.
You can use an ohmmeter to check for continuity between each of the battery terminals and the two required wires inside the switch unit
(one of the horn switch wires is connected to "Battery +" and one of the cruise control switch wires is connected to "Battery -").
Alternatively you could wire it to the lighting feed wire so that it could be turned on and off with the switch on the throttle, or the horn feed wire so that it would only light up when you held the horn button down.
Alan
