My engine will not start?

It will not start, it doesn't even turn over. We had the starter tested, bought a new solenoid, and rewired it, but that still doesn't help. Someone said it could be a neutral safety switch, but I can't find one at any auto parts store. When you turn the key you can hear a faint click when sitting in the car, but you can't hear it under the hood. We did a bypass on the starter, the solenoid, and everything else we could, so the battery is putting out juice, but not connecting somewhere along the way to the starter. A lot of the parts in it are original so it could be some 38 year old part gone bad. I would really appreciate your help, thank you for your time.