For my particular case, I was installing an LED lightbar in the grille. I used a switched (because I didn't want a chance of leaving the bar on when the vehicle wasn't, and I don't trust my kids, lol) circuit, plus my switch is LED lit so I didn't want that on all the time. I did a bit of testing and found a nice +12V switched wire going into my heated steering wheel module right under steering column. I tapped that wire, fused it with a 1Amp fuse, ran that to a switch, then to contact 86 on the relay. I put the relay in the engine compartment and used a water resistant pre-wired harness for it. That way I was only running essentially a low power signal wire from the inside, through the firewall, to the relay and I didn't have to run any high current wires into the cabin. I have a post on here about the switch and install.
