Fuel Pump Relay
Overview (per Bob Peloquin)
The fuel pump relay isn't really a relay at all. It's a time-delay circuit which detects ignition pulses and turns on the power to the fuel pump, cutting power if the engine should stall (a safety feature).
The 3 wires at the relay are un-fused ignition-switched power (black), Ignition pulse in (blue) and fuel pump out (white).
The fuel pump relay should apply 12 volts to the white wire whenever there are ignition pulses coming in on the blue wire. If the black wire is dead with the ignition on, check the main fuse...
Connecting the sabmag fuel pump backward will definitely destroy it. There's a diode inside which clamps the reverse pulse of electricity caused when the solenoid's magnetic field collapses. This diode usually shorts if power is reversed and welds itself closed rendering the pump useless. It "may" be possible to remove and replace the diode, but I think it's built into the coil as I recall. No, you can't cut the diode out as it will then destroy the fuel pump cutout relay. Big oops!!!
Notes: Relay is sometimes referred to as the "fuel-cut relay".