Hey, I'm guessing by the time you get this you will already have your problem resolved, but generally if the fuel pump relay is melting it's because high current is being drawn by the circuit (ie the fuel pump motor is going bad).

If your '91 is like my '87 then the relay itself is the protective device and under normal circumstances you could use a jumper in it's place with no issues. If you do I would suggest putting in something like a 30 amp fuse in line with the jumper to avoid a potential electrical fire. Beyond that I would say it's actually probably time to replace the fuel pump. Again, if it's at all like my '87 then the fuel pump is pretty easy to replace.