This machine can be set to different "award" modes when the player achieves a high score or playfield special: traditional credit mode, add-a-ball mode and novelty non-award mode. There is a 3-plug jack either in the main cabinet or backbox where you can change the award mode.
The schematic is available at IPDB:
https://www.ipdb.org/files/1157/Bally_1975_Hi_Deal_Schematic_Diagrams_paginated.pdf