Originally Posted by firecapt
I am wanting to hook up an LED auxiliary backup light. I do not intend to splice into my existing backup light wiring as I don't want the light to come on every time I shift to reverse. So since it will have it's own wiring and switch, is it necessary to install a relay?
Anyone feel free to correct me where I'm wrong, as I'm in the process of learning myself. The requirement of the relay is dependent on the current draw of the lights and how high the switch is rated for. For example, if your lights will draw 2 Amps, and you have a 3 Amp rated switch, then you should be okay, although it might be close for some people's tastes. But, if you have lights that draw 5 Amps, then you'll need a switch capable above that, which might be say a 10 Amp switch. The cost difference between a 3 Amp switch and a 10 Amp switch could be $15-20 ( and would reduce your selection of switches available quite a bit), which means you might as well put an relay in.
The other reason for the relay to get direct power to the light without the length of wire going through to the switch and back. If the light is in the front of the vehicle, this could be significant and will result in lower voltage drop.
The ideal way to run it would be using a switch and relay. When using a relay, because it has such a minimal draw, it would work with almost any size switch.
Whichever path you take, make sure you put an inline fuse close to the battery.
I'm debating the same thing with myself on a backup camera that draws about 300mA. Seems to make things more complicated(more stuff to break) by adding a relay.