Ok, so I would be assuming you have an early evolution that used the old button starter, which was basically a switch and solenoid all in one. To change that to a key start, you will need to add a bunch of wiring. Key switches cannot handle cranking amps and so use a solenoid. So you will need a key switch, which are easily available, you would just want a standard 5 pin indak style, then you will need a standard starter solenoid, then you will need to run wires through the switch to activate it. Then if you want it to shut down on the key you will also need to run a wire from the kill wire on the engine up to the key switch.
All do able, but not a 5 minute job.
