RJ12 & RJ25 Connector

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Summary: The connector was originally used for telephone equipment. The RJ means Registered Jack. For DCC, it is commonly used for throttle network connections, such LocoNet and XpressNet.

The six conductor connector (sometimes only the center two or four are used) that is typically used for connecting telephone equipment. Widely used in DCC for bus connections and cab plugins.

The RJ11, 12, 14 and 25 are the same physical size, the difference is the RJ12 is a 6 position, 6 conductor device (6P6C). See the LocoNet article for more information on the RJ connector series.

The RJ12/RJ25 are used to make a throttle network cable. The difference is in the wire type used:

  • RJ12 is for solid wire
  • RJ25 for stranded wire

Using the incorrect type for the wire being crimped onto will result in problems later. The "stabs" on each pin are designed for a specific wire type.

Uncrimped rj-45 connector close-up.jpg


To identify the pins, hold the RJ connector with the tab facing down, and the opening for the cable facing you. Pin #1 is the leftmost pin.