Here is a great link explaining the whole changeover. I remember having done this to the original MudRaider, an 87 auto truck. Someone explained it at the time, maybe LordTrunks, I dunno, but it was basically resistance in that 18ga or 20ga wire running from the ignition switch, over to the starter. The power going thru wasn't enough to kick the started. It seemed like it took maybe a half hour to do. I'm pretty sure I used a 3 position solenoid. I took the original spade connector off the starter and connected it to the small ring terminal on the Ford solenoid.which was mounted on the wiper motor transmission cover right there by the battery. Then i ran a 14ga wire from one of the bid ring terminals on the solenoid, down to the starter, connecting it to the .250 spade terminal. The other big ring terminal i ran another 14ga wire from the battery to the other big ring terminal on the Ford solenoid. Here is a good article about it.

https://startersolenoid.net/how-to-wire-starter-relay/