A loco without horn would be unallowable as a lead unit, but shouldn't matter as a trailing unit.
Its been a while since I retired so I'm not certain about this but the usual FRA inspection stance is that "If its equipped then it must be working". I have a feeling that a loco with a missing horn (but still has the horn valve/switch in the cab) would be considered defective at the next daily inspection or repair point? ...
Yeah, I'm not positive on those details. Back around 1980 I remember that the FRA came out with a rule that all locos used in road service that might involve switching had to have lower steps with 9" horizontal clearance so a crew person could stand on it without leaning. Some older locos were modified to conform to this requirement but locos like the DD40's were just not practical to modify, and were then sometimes restricted from service as a lead unit, I think.
If a locomotive lost its headlights I don't think it would be banned from service or required to be hauled dead, it just wouldn't be allowed to lead a consist until repaired?
