unless your fuel system has been upgraded and return line increased as well as fuel regulator you dont want to run off the one relay because both pumps will be running and at idle the volume will overwhelm the stock setup (expect base fuel pressure to be over 55psi with both pumps on )
you want to run it staged and to do that use a hobbs so it only activates the second pump when its needed (usually above 12-15psi but depends on build and return line ability to keep the fuel pressure from spiking and the motors needs)
the hobbs alone is how red used to run them and they should be fine that way but ive tested a few that wouldnt provide full voltage until over 25psi even though contacts closed at 12psi, so run a relay which will take the load off the hobbs.
run a seperate 10ga wire from the second pump connection to the front of the car by the ps pump.
connect that wire to a 30Amp relay terminal 87, run terminal 30 of relay to alternator with 10gauge wire and inline fuse (25A). that covers the pump power in and out of relay
connect relay terminal 85 to ground (this is for the coil of relay).
for the control of relay it needs a staged switched 12v source ....
get a hobbs switch that has adjustment range to 12-15psi and can be setup N/O (normally open)..ebay has them cheap but i like the adjustable hobbs that has screw terminals to connect wires (napa balkamp line or racetronix).
if hobbs has more than two terminals run common leg of hobbs to 12v (can be switched or constant but you could connect with a spade terminal the fuel prime wire by alternator since that has no load anymore with hotwire on first pump)
run other side of hobbs (n/o terminal) to the relay terminal 86
connect hobbs to a manifold source ( tee into the emission canister at steel line feed behind alternator )
make sure the hose is in good shape and ziptied
