Wiring system

A wiring system that is installed in a vehicle, the wiring system comprising:

• an electrical junction box;
• a standard harness electrically connecting the electrical junction box and a standard device;
• an expansion harness electrically connected to the electrical junction box;
• and
• a single standby connector connected to a single connector attached to an end portion of the expansion harness,
• wherein the expansion harness does not have any branching connection section at an intermediate position of the expansion harness in a length direction thereof, is not physically connected to the standard harness, and is provided independently from the standard harness, and
• the standby connector is not used at an initial stage, and is electrically connectable, through connector connection, to an expansion unit to be retrofitted to the vehicle, and
• the expansion unit includes at least one expansion device,
• when the expansion unit includes one expansion device, the expansion device is connector-connectable to the standby connector, and
• when the expansion unit includes a plurality of expansion devices, the expansion unit further includes a joint connector electrically connected, through connector connection, to the standby connector, and the expansion devices are connector-connectable to the joint connector.