The vehicle-mounted connecting wire harness with the self-detection function comprises a mounting block, a quick connecting mechanism and a loosening alarm mechanism, a plug is arranged in the middle of the front end of the mounting block, a wire harness is arranged in the middle of the rear end of the mounting block, and the quick connecting mechanism comprises a sliding groove, a connecting block, a locking block, a limiting column and a first spring. The sliding grooves are formed in the front side of the interior of the mounting block, the connecting blocks are connected to the interiors of the sliding grooves in a sliding mode, the locking blocks are arranged at the outer side ends of the connecting blocks, the limiting columns are arranged in the middles of the opposite outer side faces of the connecting blocks, and the looseness alarm mechanisms are arranged at the upper end and the lower end of the mounting block correspondingly. The wiring harness is simple in structure and convenient to use, can be quickly mounted and dismounted, is convenient to overhaul, is also provided with a high-temperature and loosening falling early-warning mechanism, can timely detect and remind when the wiring harness is abnormal, and greatly reduces the occurrence of potential safety hazards.