To find out what is required as to draw on any certain relay, go to the Device it supports ... read the data plate and see what the draw is..THEN note the gauge wire, compare that and the length of the run against a National AWG chart..
Do not use a relay LOWER in value than the device or wire gauge..
The SAME info may be present at the fuse panel, at the device fuse..
I'm betting for what you are needing, any 30 amp relays with a matching footprint will work just fine..
Only when you get up into cooling fans and the like do your relays go high current due to startup and spike conditions as well as wind resistance and rotor lock.
Headlight circuits use higher current relays as well.