We need not go so deep into this that we identify each of the 27 pins and wires by number. But . . .
the m-u jumper connects locomotives by low voltage electrical signals to control the following:
- Generator field (the "ignition key" - without it there is no traction power)
- Direction of movement
- Throttle Position
- Forward sanding, reverse sanding
- Rear headlight Off/Dim/Bright
- Dynamic braking control
- Fuel pump
- Low voltage control (contactors, relays. etc.)
All locomotives in the consist receive the same signal via the 27 pin jumper cables. How they actually use it varies, especially between older locomotives and microprocessor controlled locomotives.
