Locomotive Interface/NMRA Connector Wiring

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Pin Assignments by Wire Colour
These Connector Types are now Obsolete.
Pin # Small, Six Pin Medium, Eight Pin Large, Four Pin
1 Orange Orange Grey
2 Grey Yellow Orange
3 Red Output 3 / Aux 1[1] Black
4 Black Black Red
5 White Grey N/A
6 Yellow White
7 N/A Blue
8 Red

Six and Eight Pin Interface

Six Pin Socket Interface
Reference S-
Pin Description Colour
1 Motor (+) Orange
2 Motor (–) Gray
3 Right Rail Red
4 Left Rail Black
5 Headlight, Front White
6 Headlight, Rear Yellow
Eight Pin Socket Interface
Reference S-
Pin Description Colour
1 Motor (+) Orange
2 Headlight, Rear Yellow
3 Output 3 / Aux 1[1] Green
4 Left Rail Black
5 Motor (–) Gray
6 Headlight, Front White
7 Common (V+) Blue
8 Right Rail Red

NMRA S-9.1.1 Decoder Interfaces

Decoder Interfaces, NMRA S-9.1.1
Wire Colour Function Notes
Red Right-hand rail power pick-up: Center rail, outside third rail, traction/overhead wire to motor or interface 1
Orange Interface to Motor + (Postive)
Black Left hand rail power pickup to motor or interface
Grey Interface to Motor – (Negative) 2
White Output #1 to Front Headlight
Yellow Output #2 to Rear Headlight
Brown or
Speaker Connections 3
Green Output #3 / Auxiliary 1
Brown or
Output #4 / Auxiliary 2
Output #5 / Auxiliary 3 4
Output #6 / Auxiliary 4
Output #7 / Auxiliary 5
Output #8 / Auxiliary 6
Blue Function Common (Anode Connection, Positive) for headlights and outputs
Black w/
White Stripe
Decoder negative rail (Common ground), sink.
1 Connection to RH, center, third Rail or overhead traction wires
2 Connection to LH rail
3 Either colour could have been used prior to this definition. Either colour can be used but it must be documented.
4 Any colour other than those defined may be used, but must be identifiable and documented.


  1. 1.0 1.1 This connection on the socket (in the locomotive) may be left unconnected, or may be connected to an an accessory. If connected to an accessory, the accessory must be protected by a diode, if it is polarity sensitive, to avoid any damage in case the plug is inserted the wrong way into the socket. On the plug, this connection may be left unconnected or may be connected to connection 7 or may be connected to a decoder’s function output. In all cases, the use of this connection must be documented by the manufacturer.