I'm tagging onto this thread as I just had an issue with mine. Mine is original and has not been replaced in the past.
Out camping with a friend. Go to start after fishing, turn the key - nothing. Fiddle with the position lever (quite a bit) and it starts. Next morning getting ready to leave to fish - nothing. Fiddle - nothing. Remembering the day before, I suspect the NSS. I impress my friend using a screwdriver to activate the solenoid. We go, we fish. I start it again with the screwdriver after fishing to get back to camp. At camp, I pull out the schematic that I keep in the glove box - - - - - there is nothing in the schematic about the NSS. I pull out my multimeter and after a few minutes and some help from my friend turning the key, I figure out the terminals to jump to bypass the NSS.
Crap like this bugs me and to be honest, the lack of documentation on the schematic bothers me the most. I knew I had an original Ford copy of schematic at home as well as original manuals. I looked last night - - - there is nothing in any schematic about the NSS, ugh. I think - check out seabiscuit68 on a '74+ instead of a '73 - - still nothing on the NSS.
I attempt an adjustment using a drill bit to confirm neutral - no change.
I take it off. It did not feel right when I actuated it by hand. I bench tested it - failed continuity.
Decided to take it apart. It is not easy. There are several pot metal tabs to bend and two rivets to drill out. I took my time and got it apart. One of the sprung contact barrels was out of position and loose in the body (how, I do not know). The body was also full of greasy gunk. I completely drilled the rivets out and made through holes and cleaned thoroughly. The gasket was still there, but I added a little of silicone during reassembly. It is quite fiddly to position the two sprung contact barrels and reassemble. A couple of zip-ties and some patience and I was able to do it. Tapped the metal tabs in place and installed pop-rivets to replace the original body rivets. It felt much better when actuated and when bench tested, it worked fine. I used a syringe and put some contact grease inside via the neutral finding hole.
Installed - starting and backup lights are working properly again.
Lessons learned -
- unplug the NSS and jump the two red'ish colored wires (when looking at the NSS harness) to bypass (one above the other, one male and one female).
- even factory schematics are not complete - there is nothing showing an interrupt between the ignition switch and the starter relay.