What is a lighting relay?

Answer 1 Simply put, a relay of any kind is a remote switch controlled by another switch. Relays are usually used to control remote electrical devices which use heavy current [measured in Ampheres, or Amps]. A common example would be auxillary light systems added to a vehicle. The power supply wire would need to be very large to carry the needed current, and would have to be routed from the battery, into the passenger compartment to the instrument panel where a very heavy switch would be required. Instead, good practice is to route the heavy conductor[s] from the battery directly to the lights with a relay installed in between. Then a lighter switch would be installed in the instrument panel with wires from it to the relay. The lighter instrument panel switch and wires control the relay, which in turn controls the heavy current to the lights. This is only one example of the use of a relay. Some others are for powering high current devices such as power seats, power Windows, auxilliary devices such as amplifiers, and other sound equipment. Also. to be sure that some circuits are turned off when the key is turned off, a relay will be installed between the "hot" when key is on terminal of the ignition switch to several smaller devices. Therefore, when the key is on, the devices will be "powered up," and when the key is off, they also will be powered down.j3h