Pump start relay is typically wired up just like a normal sprinkler zone: there is a common wire, and there is a pump start relay wire (think of it as a zone wire). On other sprinkler controllers, there is often a dedicated port for pump starter relay (or master zone), on OpenSprinkler, it is software defined, and in general you can just dedicate zone 1 for it (in software you can define any zone as the master zone).