Forefront of a switch module is installed there is a collision, the module output low, there is no collision, the output high. Module aside M3 mounting holes to facilitate fixed in a small car. Lights with a switch, there is a collision, lights, no collision, lights out. Vcc 3v-12v power supply Gnd connected to power ground OUT output high and low Size:(L*W*H)3.55*2.20*0.61cm/1.40"*0.87"*0.24"