1970 Chrysler 300 - No Power

My 300 would just lose total power while I was driving. I took it into a few shops, spent good money and the problem continued. I replace all of the wiring with a Painless replacement set, which was anything but painless! The car has been running well until today except for one small issue. Sometimes when I turn the key on the starter kicks over then I lose all my electrical power. I have to get out and disconnect the battery and connect it again. I then can start it and drive away and it will not happens for days. I have a battery switch on the battery for disconnecting the power. I had the problem today, before I went out. Drove the car to 2 locations and say 20 miles. I then went to go home and I was driving along the road and just getting onto a bridge and the engine shut down. I had it towed home. At home I turned the battery off and on and it works again. Any ideas?