Motor vehicle accessory interface for transferring serial data with and supplying DC power to external accessory device

An apparatus for interfacing with a serial data bus of a motor vehicle having an on-board computer to enable information to be transferred between said serial data bus and an external accessory device to enhance operation of said external accessory device, said apparatus comprising:

• a controller for controlling the transfer of information between said serial data bus and said external accessory device;
• an accessory device communications terminal for enabling coupling of a communications cable of said external accessory device to said apparatus;
• an accessory device interface circuit disposed between said controller and said accessory device communications terminal;
• a vehicle data bus interface circuit in communication with said serial data bus and with said controller for transmitting serial data between said serial data bus and said controller;
• a DC power access terminal for supplying DC power from said vehicle's electrical system to said external accessory device;
• an ignition relay switch disposed between a battery of said vehicle and said DC power access terminal and being responsive to a signal from said controller for applying DC power to said DC power access terminal when an ignition switch of said vehicle is turned on;
• an accessory ground terminal for providing a ground point for said external accessory device;
• and
• a connection port on the vehicle data bus interface circuit comprising a connector allowing said apparatus to be utilized on a variety of makes and models of motor vehicles.