If the circuit doesn't need a switch, like HEI, don't double relay it, just go straight to it. If you are going to be turning something on and off, then add a second relay
ONLY if you are using light duty switches or you want to keep the wires small under the dash. With heavy duty switches, you can wire right off the power strip with a fuse to the switch, then out to the item you are switching on and off. I would use a resettable circuit breaker ( 30 amp )for the cooling fan and try it off the power strip. If it keeps tripping the breaker, then you will need to move the power source and up the amperage. Add a relay if you are switching the fan on and off, skip the relay if its on a thermostatic switch out at the radiator.
This is the type of circuit breakers we use at work on school buses and trucks,
https://www.etrailer.com/Accessories-and-Parts/Buyers-Products/337CB50PB.html There's lots of brands of the same type and amperage, the mount easy and will take quite a bit of over amp rush in and not trip. This type can be tripped with a push of the red button, hidden under the dash, this would make a pretty good no start security system!
