[Early_S_Man]

The keyed ignition switch can continue to supply all regular circuits, and the button would relieve the switch of starter solenoid current load ... thereby extending the life of the ignition switch by some percentage ...

I did this on a VW Type III ... starter button is on the left side of the steering column, under the dash, and hot all of the time, but it won't start unless the ignition key has been turned on!