Abstract: An audit monitoring system (10) is provided for use with any of a multiplicity of different coin operated vending machines (300). The audit monitoring system includes an interface assembly (102) for use in replacing an existing data link (330) within vending machine (300) and interfacing with row and column conductors (306) of vending machine (300). The interface assembly (102) is coupled to an audit monitoring assembly (100) which interprets the communications transferred between a controller (310), coin changer (322), bill validator (324), and motor matrix (304) of vending machine (300). Audit monitoring assembly (100) is powered from a power supply (302) of vending machine (300) and includes interface circuitry (110, 120, 130, 180, 190) for receipt of digital logic level signals, serial data or relay logic signals from vending machine (300).