I think what walker wanted was some way to provide a safety circuit on a pull start machine - i.e. one that doesn't have an electrical system and uses the magneto kill circuit to provide the safety.
The sketch (which I've redone for clarity and added the handbrake switch) is just my thoughts on a possible circuit that would fit the bill.
To be sure it would be an infuriating system, open to operator error or, given the number of switches, failure, with the result being the poor operator trying in vain to start the thing with the magneto grounded!
