(a) Specifications. Wiring for circuits shall be constructed and installed to conform with mechanical and electrical requirements not less than those recommended for automobile wiring in the 1952 or any later edition of the SAE Handbook. Required lamps shall be connected to the source of power with stranded wire. This shall not prohibit use of the frame or other metal parts of a motor vehicle as a ground-return system, provided there is adequate electrical grounding between towing and towed vehicles.

(b) Wiring Protection. Wires shall be grouped together and protected either by nonmetallic tape, braid, or other covering capable of withstanding severe abrasion or a metallic sheath or tube. Wiring shall be properly supported and located so as to avoid becoming charred, overheated, or enmeshed in moving parts. Insofar as is practical, wiring shall not be adjacent to any part of the fuel system. Unless the wiring is metal covered, the edges of all holes in metal through which the wiring passes shall be rolled or bushed with a grommet of rubber or other suitable material.

(c) Wire Size and Connectors. Wires shall be of sufficient size to eliminate excessive voltage drop and to prevent overheating. All joints shall be soldered or fastened both mechanically and electrically with equally effective connectors and shall be insulated. Voltage at the bulb sockets when lamps are burning shall be at least 85% of the design voltage of the bulb with the engine running.

(d) Detachable Connections. The electrical wiring of detachable connections between towing and towed vehicles shall be contained in a cable, cables, or other substantially constructed protective device, and shall be mechanically and electrically adequate and free of short or open circuits. Suitable provisions shall be made for the prevention of an incorrect connection or an accidental disconnection. Any detachable connection made by twisting wires together from the towed and towing units is prohibited. Wires or cables shall have sufficient slack to accommodate all normal motion of the parts to which they are attached without damage to the connection.

(e) Spare Fuses. Each combination of vehicles or each motor vehicle if operated singly shall be equipped with at least one spare fuse or other overload protective device, if the devices used are not of a reset type, for each kind and size used. In driveaway-towaway operations, spares located on any one of the vehicles will be deemed adequate.