Buckblaster

Looking for tips on bleeding dual brake system. My 75 M20F has 4 master cylinders, I repacked all 4, blew brake lines from master cylinders to calipers out with shop air, wanted a clean start. Reinstall master cylinders, hooked up pressure pot (max 15 psi, i did not carbonate fluid, been using pressure pot very long time…) and as per manual depressed the pedals I wanted to bleed. Worked fine on pilots side. Manual say to depress CP pedals to sequence shuttle valve,,,, so I depressed CP pedals and bled both sides again, nothing… dead pedals on CP side, GTG on pilots side. I tried it with about a gallon of fluid. I believe there is an issue with my shuttle valve. I didn’t see it as I removed every belly panel (location?). Help please… thanks, Paul

Can you share the wiring manual? I'm about to get into a 75 F model that has been parked for 5 years. Anticipate the same issues.