g'day stingray.
The starter motor is energised via a mechanical safety switch as you know,
to operate the starter you have to push the Gearstick into Start Yes.
The gearstick is connected to the manual start solenoid by a link rod and a 90 degree elbow,to access the start solenoid ,under the battery and bolted onto the clutch housing by four bolts, one bolt has the Eath/ground wire attached be sure to replace it when you are done playing with the switch.
disconnect the battery ,remove the four bolts lift the solenoid up and slide a srewdriver under it to hold it up then remove the small split pin and clevis that connects the operating rod to the switch, remove the switch and give it a good clean .
the switch can be stripped down and repaired ,the most common problem is the Copper contacts these can be bought from an auto electrical shop Best to find a shop that has een in business for at least sixty years otherwise you may get the runaround, when repaired refit the switch ,if you look closely the four retaining bolt holes are elongated this is to allow you to adjust the switch, it wll need alittle bit of Fiddling to get the switck in the correct position.
Happy Days.
Hutch.