Oil pressure switch isn't tied into the ECM, although it's power feed is the same as the fuel pump relay, so if there is something wrong with it's wiring, that could affect that fuse.
You can unplug the oil switch...it could be two wires, the gauge sender is one wire. I *think* yours being a '91 will have a three wire sender/switch though, which just means you'll lose your oil pressure gauge for a bit. It will still start and run fine IF the relay and it's wiring is good. If the fuse still pops, you know it's not the switch.
Conversely, you can disconnect the fuel pump relay and the engine will still start/run, assuming the oil pressure switch is working right, and you have more than 5PSI oil pressure. It will take more cranking before it starts though, of course. Quick check for both of them.
