If you have time (ie. the donor car is yours) remove the dash and follow every wire. You'll find that all wires will lead to such things as the headlite switch, gauge cluster, ac controls etc...
If you are pressed for time (at the junkyard or the mrs. wants it gone) yank the dash, take what you need and then return whats left to the junkyard.
1991 caprice was throttle body fuel injection which makes it a little easier. It only requires about 9lbs of fuel pressure. You could get fancy and use the in-tank fuelpump or just snip the harness close to the tank (s/b 3 wires, 2 for +/- pump and 1 for fuel level) use an after market frame mounted pump using these leads.
Be sure to get the computer, all underdash wiring and switches, the fuel pump wires, fuse block and what ever else looks important.
Hope this helps you alittle.
Scott
