An interlock was needed to allow for a yacht to have a start switch that was interlocked with an ignition switch with the additional requirement of preventing the stop switch being interlocked with turning off the ignition. In this diagram the middle switch is a double pole double throw (DP-DT) with one of the throws shutting down the circuit and the other firing the solenoid to kill the engine. A secondary circuit (not shown) ensure the kill switch is fired for a minimum amount of time to prevent the engine continuing to run with the ignition turned off.
A green LED shows that the engine breaker has powered the circuit. When the ignition is on there is a red LED. The starter solenoid is indicated by the lamp.
