Gravely walk behind repower

[Rpsaffa]

I have a gravely pro 150 that had I Kawasaki fb450v-ms14 pull start. I bought a new Tecumseh ov358ea electric start. You can see the problem that poses. The gravely has a 2 pole ignition switch with 3 wires. 2 going to the machine and one spliced going to the old coil. The new tecumpseh has a green yellow and red coming off the starter. I can find what tractor this engine goes to as it was bought new in box off fb market place. 2nd why does a recoil start need an ignition switch. For the safety’s I’m guessing? Would I just need to phrase the ignition switch and splice into the new harness. I’ll post some photos. I’ve rebuilt plenty of engines just nothing that has a wiring harness. Chainsaws mowers trimmers etc. if you have experience please guide me in the right direction or even to a book or pdf that explains how these wiring systems work. I’ve searched high and low and with no luck.