Two easy bits of information you need to know. The original switch had (I believe) five pins.
1) using a wiring diagram or simply continuity checking a good original switch make a simple diagram. Number switch connections.
So key off...continuity pin 1 to 3.
Key on...continuity pin 1, 2 and 4
Key start...continuity pin 1,2, 4 & 5.
(Of course, for illustration, but easy to do)
2) now you see pin 1 is red wire, pin 2 green, etc.
Now find a universal switch, local NAPA or auto parts store or if ordered a switch with same continuity each position, same as original. Universal switch will have solder terminals, screw lugs or 1/4" male posts.
Cut original wires close to switch, then solder to new switch, or screw lugs or 1/4" female jacks. Then simply plug in as original.
It's very easy you just need replacement switch same number of terminals and same continuity each position.