During the operation of energy storage systems, harness failure is a highly prevalent and concealed fault. The fault manifestations are highly similar to those of BMS mainboard, sensor, and controller equipment failures, making it extremely easy to cause misjudgment and missed judgments, leading to operational and maintenance rework and hidden dangers. Common faults in energy storage harnesses are mainly divided into six categories: insulation aging failure, poor line contact failure, signal interference failure, harness damage and short circuit failure, voltage drop abnormality failure, and corrosion aging failure. Each type of failure has its own unique characteristics. Standardized troubleshooting methods can accurately distinguish between harness issues and equipment issues, improving the accuracy and efficiency of energy storage operation and maintenance. The first category is insulation aging failure, which manifests as system reports of insulation faults, ground leakage, low insulation resistance, and frequent triggering of insulation protection shutdowns. Many operation and maintenance personnel will directly determine it as cell leakage or BMS detection module failure, but in reality, it is mostly due to aging, damage, moisture, and electrolyte corrosion of the harness insulation layer, leading to insulation performance degradation and ground leakage. The troubleshooting method is to disconnect all equipment and test the harness insulation resistance separately. If the resistance is not up to standard, it can be determined as a harness failure, otherwise it is an equipment failure. The second category is poor contact failure, which manifests as large voltage fluctuations in the battery cluster, intermittent connection and disconnection, unstable charging and discharging power, and random reports of disconnection faults. The root cause of the fault is poor connection, loose crimping, and oxidation of the harness terminals, leading to unstable current transmission. The core characteristic that distinguishes it from BMS failures is that the fault is irregular, and the probability of failure increases significantly when shaking the harness, experiencing temperature changes, or vibrations. Restarting the system cannot completely eliminate the fault, but the fault immediately recovers after tightening the terminals. The third category is signal interference failure, which manifests as voltage sampling jitter, temperature data drift, CAN communication interruptions, data garbled, and system false fault codes. This fault is mostly caused by the mixed distribution of strong and weak electricity, poor grounding of shielded harnesses, and damage to signal harnesses, belonging to harness wiring and protection issues; while BMS equipment failures manifest as abnormal data at fixed points, continuous faults, and no interference fluctuations. Through separate shielding and isolation of the harness, and re-grounding testing, if the fault disappears, it is a harness interference issue. The fourth category is harness damage, short circuit, and open circuit failure, which manifests as complete lack of voltage and data in the corresponding battery cluster, direct system reports of short circuit and open circuit faults, and equipment unable to go online. It is mostly caused by construction wear and tear, squeezing, bending and breaking, insulation damage and short circuit, and multimeter continuity testing can directly determine the harness continuity abnormality, completely distinguishing it from equipment failures such as equipment freeze-ups and module damage. The fifth category involves abnormal voltage drop faults, characterized by a large voltage difference during battery cluster charging and discharging, low terminal voltage, insufficient power output, and high temperature rise. These faults are primarily caused by insufficient wire harness diameter, excessively long wiring, conductor oxidation, and excessive contact resistance, which are issues related to wire harness selection and aging. Equipment faults with voltage differences are often due to consistency issues among battery cells, which can be accurately distinguished through segmented detection of line voltage drops. The sixth category concerns corrosion and aging faults, manifested as swollen and cracked wire harness sheaths, blackened and oxidized terminals, accompanied by various intermittent faults. These are caused by corrosion from electrolyte and moisture, which are issues related to long-term aging of the wire harness. The overall troubleshooting logic is as follows: first, power off and inspect the wire harness for continuity, insulation, voltage drop, and shielding grounding. After eliminating potential hazards in the wire harness, proceed to inspect the BMS sensors, mainboard, and module devices to completely avoid misdiagnosis and accurately resolve various abnormal faults in the energy storage system.