1950 Ford O.D. Help

I've Got A 1950 Ford With Over drive I Was Told That The O/D Worked Until They Put A SBC In It With A HEI Ign System. As I Remember The Neg Side Of The Coil Was Nothing But A Interrupter To Take It Out Of O/D.But It Will Not Work At All The Solenoid Works OK The Gov Closes To Ground But No Go?? Can Any One Help Me Out.
Thanks

 

Change made from Pos to Neg ground when they put the SBC in? Everything get swapped around? I've been known to overlook more obvious stuff before..........