the light relay, no all cars have them... i dont even know if my car has it lol. but i know some have it and sometimes they go bad


for the other kind of relay... a relay in general is like a remote activated switch.

small box, 4 terminals.

battery positive goes to one terminal, and another terminal goes to the ballast to give it power.

the other 2 terminals are signal. one is the low beam power, and the other terminal is ground.


so in simple. when you turn your low beam on, it sends a signal to the relay to switch on the power circuit