49 CFR 229.89 - Jumpers; cable connections.
(a) Jumpers and cable connections between locomotives shall be so located and guarded to provide sufficient vertical clearance. They may not hang with one end free.
(b) Cable and jumper connections between locomotive may not have any of the following conditions:
(1) Broken or badly chafed insulation.
(2) Broken plugs, receptacles or terminals.
(3) Broken or protruding strands of wire.