Main Switch Operation

When the ignition switch is on, current flows from battery to the main switch. When the main switch is turned on, current flows through the main switch to the body ground, and then turns on (closes) the relay contact in the main switch. As a result current flows from the main switch so it is supplied to the cruise control Electronic Control Unit (ECU). Also current flows lighting the power indicator to the main switch of the ECU. Therefore the main switch remains on and continues to supply current to the ECU.