Wire it as a circuit so that the buttons (when pressed) complete the circuit from the positive charge sent down the wire from the 9volt battery to the resistor in the bottle neck. You need 1 inside accessible by both the crew and one outside for the scruit's.

Remember they have both battery check and arming system circuits in the box.

If you get stuck and the cars driveable Im sure we can do this for you (were 1 mile from 3 sisters)

Andy there are no rules on spaceframed cars with an engine originally designed for the car. (Metro 6R4's still run under this rule). The trouble came a few years back when things like The Plants Reliant Kitten appeared with spaceframed light chassis and motorbilke engines. Looks alot of work tho'