Mike,
Do you know how much of a load can the inertia switch handle? My recollection is the factory wiring can only handle 15 amps of load but I have no idea what the inertia switch can carry.
When I moved up to a 255 lph pump I used the pump side wiring off the inertia switch as the trigger for a Bosch 30A relay. Relay is fed by a fused 10 ga wire to terminal 30, 12V+ to the fuel pump is wired to terminal 87, inertia switch 12V+ goes to terminal 86, and terminal 85 goes to ground.
The pumps are voltage sensitive so the better supply you have to them the better they perform.