How a Starter Disable Relay works to disable the starter of a vehicle with one wire. The controller interacts with the relay by grounding its output to the relay to disable the starter (open circuit output to starter).
In this layout the Momentary Pushbutton represents the Key/Ignition Switch and the Lamp represents the Starter. The controller is the SPST switch on the right side. The vehicles existing Starter Wire is "cut" and then reconnected through the relay. The relay operates in a "normally closed" state, allowing current to freely pass through. It's only when the controller "grounds" the relay that the relay "opens" and disables the output to the starter when the ignition switch is engaged.
