Just buy the usual ones on Amazon, there good to like 30 amps and that's more than enough for just about everything, if your going to need more than that it's going to require a huge ass relay, like a starter solenoid or something

Nilight 50003R Automotive Set 5-Pin 30/40A 12V SPDT with Interlocking Relay Socket and Wiring Harness-5 Pack, 2 Years Warranty https://www.amazon.com/dp/B0748F1JK4/ref=cm_sw_r_apan_i_X8WKVM99P2TC7ETNNJ9Q?_encoding=UTF8&psc=1

These are the ones I used