1) Run an Alligator Clip jumper wire from the transformer's terminal 8 with thick yellow wire(s) to the yellow wire on the right flipper button.

2) And run an Alligator Clip jumper wire from the 10 amp fuse with thick black wire(s) to the red wire on the bottom right flipper solenoid.

3) If the bottom right flipper starts working, the problem is in the electrical feed, and not in the flipper mechanisms.