I agree, it sounds electrical.
During all the fussing about the offending circuit gets manipulated enough to make a good connection.
After it sits, corrosion sets in and, nada.
The proper procedure is to check the voltage drop in each circuit to the starter.
Battery+ to starter
Battery+ to switch
Switch to starter
Battery- to engine
Use a digital voltmeter, set to DC, with the leads attached at each end of the circuit. (to form a parallel circuit with the meter)
Energize the circuit, turn the key, and look for a voltage reading at the meter. Any reading over 1.5 volts DC indicates a poor connection, dirty connection or crimp.
Reading of 12 volts, or battery voltage indicate an open, broken circuit.
Do this for each circuit.
Hopefully this makes sense.
Also verify the engine crankshaft can be rotated manually when the starter is not working.