Not sure how to go about testing, the FSM might have some info on that. If the wiring to your alternator is hard and brittle you can expect the same throughout the harness. New is always the best option and Wiring specialties sells a replacement for about $150. You don't need to pull the engine the process is fairly easy to do. From my experience only the ps accordion hose will need to be removed and the rest can be accessed from underneath.
From above, unplug the 4 connectors I mentioned earlier and remove the plastic clip located under the ps reservoir securing the harness to the body. From there it ties to a bracket on the side of the head and down to the alternator. Mark the harness where it ties to the bracket before removing it. Once the old harness is removed lay them side by side and transfer the mark to the new harness. This will ensure you've given yourself enough slack to make all the connections without putting too much tension on the wires. Next crawl underneath the car, remove the 3 connections on the alternator and the plastic clip securing it to the motor mount. Unplug the oil pressure sending unit and starter. There's another bracket securing the harness between the oil filter and starter, mark and remove the ties. Lastly, remove the 3 connectors are on top of the transmission. Patience goes a long way here, these are a PITA and fixing a broken connector usually means dropping the trans. There's an elbow at the beginning of the harness so don't try an yank it out from underneath it has to be removed and installed from the top. Installation is pretty straightforward.