1969 Oldsmobile Cutlass Engine won't start.

I tried replacing the starter three times, and the alternator, and the external generator. The problem is in the wireing. The wires connected to the starter are taped up with electrical tape, and they don't seem to working right. What should I do? My mechanic said that there is a loose wire that goes to the ignition if that helps. My lights on the dash board light up, and when I turn the key it makes a clicking sound. Before this problem when it ran, I would run the engine for a while then turn it off, but it has to sit awhile and cool off before it will start again. I replaced one of the connectors on one of the wires that goes to the stater, this still did not help.
Thank You
D.P.