is the main relay up behind the driver shock tower interchangeable between s4/s5 and na/turbo?

 

Yes, they're all the same. If yours is acting up, you can substitute in two regular 40A relays by wiring their coils wired in parallel. That means both Pin 85s are together, and both Pin 86s are together. Consult the Wiring Diagrams/manuals on Foxed.ca for wire colors. Sure beats paying $100+ for a new relay.