A field device I/O connector includes a base and an I/O module removably mounted on the base for transmitting I/O signals along an I/O channel. A set of electrical connectors mounted on the base connect the base to a field device. The electrical connectors, the base, and the I/O module mounted on the base cooperate to define the I/O channel. The I/O channel includes a conversion circuit to convert between I/O signals and a digital data format output from the field device I/O connector. The base and I/O module also cooperate to define a diagnostic circuit connected to the portion of the I/O channel extending through the I/O module. The diagnostic circuit extends to a diagnostic logic circuit that may be included on the base, in the I/O module, or away from the field device I/O connector.

A field device I/O connector includes a base and an I/O module removably mounted on the base for transmitting I/O signals along an I/O channel. A set of electrical connectors mounted on the base connect the base to a field device. The electrical connectors, the base, and the I/O module mounted on the base cooperate to define the I/O channel. The I/O channel includes a conversion circuit to convert between I/O signals and a digital data format output from the field device I/O connector. The base and I/O module also cooperate to define a diagnostic circuit connected to the portion of the I/O channel extending through the I/O module. The diagnostic circuit extends to a diagnostic logic circuit that may be included on the base, in the I/O module, or away from the field device I/O connector.

Provided is a wire harness which does not increase in size with increase in number of electronic devices controlled by an electronic control unit and can standardize a relay connector, and an electronic device control system including such wire harness. A wire harness structure (2) communicably-connects electronic devices (3) mounted on a vehicle to an electronic control unit (4) controlling the electronic devices, and includes a relay connector (6, 6A, 6B) relaying a control signal from the electronic control unit to the electronic devices, a power wire (81) and a ground wire (82) drawn out from the relay connector, power supply units connected to the power wire and the ground wire, and sets of signal wires (83a, 83b, 83c) transmitting the control signal to each power supply unit arranged to supply power to the electronic device and drive the electronic device according to the control signal from the signal wire.