Rule 17 refers to how a locomotive engineer operates the locomotive's headlights while running the train.
Rule 17 is part of a railroad's standardized rulebook.
Rule 17 varies from railroad to railroad. Typically, it requires dimming the headlight when the locomotive is standing in a siding waiting to meet another train, passing through passenger stations or moving within yard limits.
Program CV49 to 104 to set Function 0 to implement Rule 17 dimming.