If they work on self test which is a CPU controlled activation, then from CPU onwards is OK... your problem most likely is with the signal coming  from the PF... Been a while since ive worked on Bally/ Stern, but nake sure that whatever switches are required to activate WOW are operational and making closure ( test with a meter).. follow these to the driver board and make sure signal is there... if this is OK, then you have a driver board problem.. normally a decoder IC which sends the signal to the CPU and most likely some sort of buffer chip.. 74XX etc