Wire harness manufacturers use wire harness loop testing equipment to detect open and wrong circuits in the wire harness. We usually use this as a wire harness loop testing station.
Manually use a homemade tool according to the drawings, which we call a conductor (it can be modified with a doorbell and remove the doorbell switch. One end is the positive pole and the other end is the negative pole) as long as two or more points of the wiring harness ( The open circuit or wrong circuit of the wire harness can be judged by whether the welding wire) is connected at the designated sheath hole position. (This method is often manual testing during trial production of new products)