If you hear a click fron the solenoid, it's not the neutral safety switch. It could be the starter itself. Mine gives me problems when the temp is around freezing. If your wiring harness is turning into toast, this is probably your problem. not enough juice to the starter from a bad ground. There are two small wires with spade conectors going to your starter, these were the ones on mine that melted when my harness burned up. The heavy guage battery/starter cable end may have some corrosion on it too. You will have to get under the car and take a good look at the condition of the wires. (drivers side B21 Motors). You may be able to splice in a new section for a temporary fix. Also check the battery cables. The ground that goes to the body and to the engine block could have corrosion on it. I cleaned up the ends of mine with sandpaper for a good contact.
Ben