The NSS is not going to keep the electrical power from the entire truck, only the starting circuit.
ConstantFix- a quick way to determine if the NSS is faulty is to unplug it and toss in a temporary jumper in the plug. Some consider this dangerous since the vehicle WILL attempt to start in gear.
Please correct me if I'm wrong, but I thought the manuals only had the "clutch switch". When I did my 5spd swap I only remember doing three splices, the clutch start switch, something for 4x4 and the NSS. Think I did the NSS because the plugs are different. Guess I just answered my own question
gannonrt- The battery terminals are a good place to start. Just as likely though is a bad ground. When you get that multimeter go ahead and check every fuse, not just for continuity but read the voltage. You may also want to remove and reinstall them all just to establish clean contact.
Good luck bro