Could be the relay - Check for dry joints - Here's the path of the 43VDC for the flippers

J1 Pin 8 - To left flipper coil from Pin 4 of Relay
J1 Pin 9 - To right flipper coil from Pin 3 of Relay

J2 Pin 1 - To right flipper switch from Pin 5 of Relay
J2 Pin 2 - To left flipper switch from Pin 6 of Relay

It is a simple circuit, you may need to visually check the relay - It might be in a socket and if there is another Bally machine close by, you can swap them out. Check J1 and J2 on the solenoid driver board - refit just in case !