This IS '91.......do not know for sure if there were any alterations in the wiring configuration.
ess
essentially the relay just reverses the current flow thru the door lock motors to command them to open or close.
You'll need to get your hands on a wiring schematic for the vehicle, preferably the factory manual to detail the system characteristics, I take it you're thinking of something like a Viper 1 way entry system?, they usually include their own rough schematic for tapping into the car's harness.