Wiring up a reverse motor

[flyerncle]

Put a seperate braided earth on just in case and as TT says fit a relay to the solenoid feed that isolates it from everything unless its in neutral and dont forget to include the handbrake switch.
Personally I would use a press button switch and not a rocker switch as this would allow you more control in reverse, as you know dipping the clutch wont stop it. May save embarrasment/damage at a later date.

I have worked on many "kit cars" (Lotus/TVR/etc) over the years and relying on chassis earth is somtimes not too reliable.