First, Be sure the ampacity of your switchgear is capable of handling the task of energizing the solenoid..If not you may need a relay.
Second, Find a SWITCHED 12 volt source, on in "RUN" (heater or wiper fuse might be good if 25 to 30 amp fuse).Run a 12 or better 10 gauge wire. If you don't have that, or don't want to hack the harness, add a relay, thus:
- Relay Coil#85 = To any fused switched source at the fuse buss over an amp. 18 gauge wire.
- Relay coil#86 = to hard , properly bonded ground. 18 gauge wire.
- Relay contact #30 to the Start Button 10 gauge wire.
- relay contact #87 to the main terminal on the starter solenoid (battery cable bolt) Via a proper fuse link or MAXI fuse. 10 gauge wire.
- Relay Contact #87a will not be used.
The other side of the push button will go to the neutral safety switch, and on to the "S" terminal on the solenoid.
Either configuration will give you an active pushbutton in "ON" only..and not when the key is off..a safe way to go.