The relay needs to carry out different derating designs according to different loads. Control lines from the ECU are required, and the output lines are then pulled to the electrical equipment, which increases the wiring harness loop and increases the cost. Open-loop control, can’t monitor, can’t diagnose, you may not know if it’s broken. Due to the long wiring harness of commercial vehicles, affected by the stray inductance of long wires, the relay switching will generate some high-voltage pulses, which will cause overvoltage hazards to other electronic equipment and affect the EMC performance of the vehicle.