I will assume that you are getting 50V power from the transformer ok.
I'm not greatly experienced in working on Bally EMs, but after an EM machine boots up and all score reels and steppers have reset, there are usually 2 or 3 switches than need to trip or close in order to propagate power to the playfield (flippers, thumper bumpers, etc). I would suspect those switches are not closing or perhaps even have burned contact faces (since the ?popup? solenoid presumably received continuous current which may have cause it to burn?).
Since you have the schematic, can you follow the two lines from the 50V taps of the transformer horizontally over to where they reach the section of the schematic where the flippers and thumper bumper solenoids are depicted? Looks for 2 or 3 switches in the path. I don't have the Trail Drive schematic, but if I go on IPDB and reference the schematic for a 1970 Bally El Toro, there are switches in the Game Over trip relay and in the Reset relay, which need to close to deliver power to the playfield. They can be seen in section F24-F25 on the El Toro schematic. Looks on your schematic for something like that and then examine those switches for conductivity and no broken off wires.
El Toro: https://www.ipdb.org/files/772/Bally_1972_El_Toro_Schematic_Diagram_continuous.pdf
