Lawnflite 12 HP ride on mower Model 548 Electrical repair?

I am renovating an old 548 mower to use as a garden tractor. The ignition switch is broken and I wish to replace the key ignition switch with a toggle switch for 'on' and a press button switch for 'starter.

The key switch fitting has 4 contacts with wires connected comprising two connections with red wires, a black wire that serves the ampmeter display, and a twin connection of yellow wires which appear to be safety switches. Please can you advise me of which wires I need to connect to my on/off toggle switch and which to my push button starter switch and any bridge between the two.

Graham
August 2008