...The standard auto relays work fine. There are two terminals on the low-amp control side, and three terminals on the high-amp load side. I've wired stuff up for years, but I still have to put on my reading glasses and carefully check the terminal numbers against the wiring diagram every time I wire something up. I have also run into relays that use the same socket, but the terminals are different! Always check your relay's diagram.
In the pic below, terminals 85 & 86 are your low-amperage control circuit. Your switch will be on this circuit and 18 gauge wire is perfect.
Terminals 30 and 87 are your high-amperage load circuit. I'd use 12 gauge wire here.
Terminal 87a is used when you want the relay to open a normally closed circuit, also 12 gauge in the circumstances you'd use it.
For fun, wire power to terminal 30, jump terminal 87a to terminal 85, and ground terminal 86. Congratulations! You've just made a buzzer from a relay.
Relays are not polarity sensitive, so it's up to you how to run power and ground. The standard is to use terminals 30 and 85 for (+) and 86, 87, and 87a as (-) even though the diagram below shows 86 as power and 85 as ground.
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I'd suggest running a single 12 ga wire through a 20a fuse to terminal 30 and a 3" 18 ga jumper wire from terminal 30 to terminal 85. Run from terminal 86 with 18 ga wire to your switch, and from the other side of the switch to ground. Run 18 ga wire from terminal 87 to your driving lights, and then ground the other side of the lights, and you're done.
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