Do traffic police need to set up warning signs when checking cars or dealing with traffic accidents at night?

According to the Road Traffic Safety Law, in the event of a traffic accident between a motor vehicle and a pedestrian, except that there is sufficient evidence to prove that the pedestrian violated the traffic rules and caused the accident, the motor vehicle side must bear the main responsibility. From your description, although the auxiliary police did not set warning signs or wear reflective clothes when performing official duties, it cannot be proved that they violated traffic laws. Therefore, you are mainly responsible for the accident.