Though the Relay/Power Board is not required, it is a convenience and reduces the chance of miswiring during the installation. The relay board provides a central place for all of the required relays, fuse protection, and external wiring for the MegaSquirt ECU. If you are installing MegaSquirt in a previously fuel injected engine you may be able to reuse all of your existing relays. If you are fuel injecting a previously carbureted engine you will need to install relays for the main ECU power, Fuel Pump, and FIdle circuit. You can do this manually or you can use the Relay Board to simplify this process.

Comes with DB-37 connector to be used to build your relay cable, and the "half-case" shown in the picture. The parts on the relay board are capable of standing up to an underhood environment.

Uses standard 'mini-ATO' style fuses. (not included) Recommended fuse values (from the MegaManual)

20 Amp main fuse,
10 Amp fuel pump fuse,
5 Amps fuses for INJ1 and INJ2 with a 4 cylinder engine, 7.5 Amps with an 8 cylinder.
You may need to change these values based on your needs. These are good starting values.