Review on ESUPPORT Car Marine Red LED Toggle Switch Dash 4pin Pack of 5 - Illuminate Your Vehicle's Controls with Style by Larry Simpson

The switches worked perfectly. If you look at the back of the switch with the two unused pin headers facing up, the pins on the left are for the power and the pins on the right are the test light bases. . The upper left pin is the line or power input, the lower left pin is the line out to the device controlled by the switch. The test lamp is powered from the top left pin, and the top right pin is a non-switchable ground for the test lamp. and when grounded, the test lamp is always on when the upper left contact (line input) is energized. The lower right pin, when grounded, will turn on the warning light when the unit is powered on. If none of the right hand pins are grounded, the test lamp will never illuminate and the switch will operate as an unlit single pole switch. You wouldn't connect both right pins to ground.