Are the pins #'d...???
If so, like a typical Bosch relay...do this:
85 and 86 are for the trigger/switch...one needs a positive (+) switched wire to turn it on, one needs a ground. So run your stock fuel pump (+) to one, and run a short ground to the other.
Now, run a (+) feed directly off the battery to 30...this is the power supply wire.
87 is run to the fuel pump...use the other end of the stock wire you cut, or run a new one.
See here for a diagram, maybe it will help:
http://www.6066gmctrucks.org/BoschRelay.htm
...but the idea is that you're now using the stock wiring to turn on the relay, which will then conect 30 and 87, giving the fuel pump a full 12 volts of big amps.
- Brian