Universal 12V Relay, For Wiring Accessories, Lights, Etc.

If installing accessaories like fog lights, driving lights, radio amplifiers, electric cooling fans, etc; you'll want to install a relay inline to control the battery power to those accessories, rather than tying into an existing wiring circuit.  A relay allows you to use a switch with very low amperage in order to run a much bigger load, which is a much safer way than running full power to the on/off switch.