text: Traction control The Class 73 was fitted with two separate power controllers on the driver's desk (and replicated on the secondman's side); one for electric or auxiliary power (under diesel power) and the other only for diesel power. The auxiliary power arrangement was to accommodate diesel operation when being driven from mainline EMU stock.
  Multiple working
  Multiple working is when two or more locomotives are coupled together and controlled by a driver in the leading driving position. This was achieved with the aid of the standard SR 27-wire jumper connection system, a design that ensured excellent compatibility. They could work with other 33/1, 71, 74, locomotives (in fact any type 2,3 or 4 blue-star coded mainline locomotive) and EP multiple unit stock.
  In order for the Class 73s to achieve their maximum versatility, the locomotives also had to have multiple brake systems. When built in the 1960s, this required vacuum brakes for use with freight, most locomotive-hauled carriages, and many other locomotives, including steam; also air brakes for use with the newest BR-designed wagons, and newer types of passenger carriages and locomotives; and, for use with the Southern's electric and diesel multiple unit fleets, the Electro Pneumatic Brake (EPB).
  Class 73/9 variants have been fitted with the AAR system, allowing for multiple working with Classes 59, 66 & 67.