Welder power cord is a "NEMA 6-50". It has 3 prongs: round prong located top-center, with a vertical flat blade on each side (one side is "taller" than the other). On the Generac GP7500e generator, it has a 4-wire outlet called "NEMA L14-30" for 240 volt supply. I made a short extension cord with correct plugs/receptacles to physically match up, but can't figure out where the wires go. How do the 4 wires at the generator get reduced down to 3 wires at the welder plug? And do I have to connect a ground wire from the generator frame to a pole in the ground to make this work? I can send pictures if there is a way to do it on here. Thanks!

Electrical Supplies - Diesel - Miller 907218 Trailblazer 302 Welder Generator