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). The interface assembly (102) is coupled to an audit monitoring assembly (100) which interprets the communications signals transferred between a controller (310), coin changer (322) and bill validator (324) 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) for receipt of digital logic level signals, serial data or relay logic signals from vending machine (300). Additionally, the data retrieval terminal (20) may be removably coupled to the audit monitoring assembly (100) through either a hard wired coupling (254) through a serial interface (250) or alternately by means of infrared optical signals (12, 22) through an infrared interface circuit (260).