Suppose that one wire provided power to a controller, motor, or helm-to-rudder communications. Rudders are too big and require too much force to be positioned by muscle power..
the wire in question connected the 6600 volt board to the 440 volt board step down transformer. transformer breaker tripped on loss of 6600 volt input. The 440 board provides power to the main engine fuel, oil, & cooling pumps. It also powers the steering motors.