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This page is only provided to satisfy curiosity needs. If you need to check these colour codes, you may not have the prior knowledge needed to safely complete this complex wiring task. The diagrams do not indicate certain requirements including indicator relays (used to prevent trailer load affecting indicator flash rate,) beepers used as trailer turn indicator warnings and fog-light switching circuits. I advise that this page should not be used! I accept no liability for any problems that may be caused by ignoring this advice.

Car 7-Pin Black (Also known as 12N)

Many vehicles and trailers in the UK use this popular connector. It allows all the main road lights to operate but it does not connect the reversing light, permanent power or refridgerator supplies. In the UK, these connections are made using a second connector. Normally, the road lights operate via a black socket and the accessories use a grey socket. Although both sockets look very similar, it is not possible to accidentally plug incompatable plugs into either socket. The pins can be labelled L, 54G, 31, R, 58R, 54, 58L but this is often simplified using the alternative labels of 1, 2, 3, 4, 5, 6, 7

ConnectorLabelColourDescription
7 pin black socket 1 (L) Yellow Left Indicator
2 (54G) Blue Rear Fog Light. Often not connected, sometimes +ve power, some sockets disconnect cars rear fog lights when in use.
3 (31) White Vehicle Earth usually -ve
(Sometimes wire is thicker than the others)
4 (R) Green Right hand indicator
5 (58R) Brown Right hand tail lamp
6 (54) Red Brake Lights
7 (58L) Black Left hand tail lamp

Car 7-Pin Grey (Also known as 12N)

This is used as an accessories socket. There should also be a 7-pin black socket (described above) to supply the trailer road lights. The pins can be labelled L, 54G, 31, R, 58R, 54, 58L but this is often simplified using the alternative labels of 1, 2, 3, 4, 5, 6, 7
ConnectorLabelColourDescription
7 pin grey socket 1 (L) Yellow Reversing Light (can link to trailer brakes)
2 (54G) Blue Rarely used
3 (31) White Vehicle Earth usually -ve
(Sometimes this wire is thicker than the others)
4 (R) Green Permanent power (usually +ve), can be used for internal caravan lights etc.
5 (58R) Brown Rarely used
6 (54) Red High drain power (usually +ve)
This only supplies power when the engine is running.(To stop high drain items e.g. Fridges, draining the car battery)
7 (58L) Black Second earth connection (usually negative)

13-Pin EU (or post 2009 UK) Socket
(also knows as 13N)

This socket, popular in mainland Europe should not be confused with the various pre 2009 UK sockets which accept either the 7-Pin black plug or patented 13/14 pin customised plugs. (Many new UK caravans made after 2009 have this wiring but it is rare in the UK before 2008.) There are many variations in the wiring colours and I have only indicated some popular choices.
ConnectorLabelColourDescription
13 pin EU socket 1 Yellow Reversing Light (can link to trailer brakes)
2 Blue Rarely used
3 White Vehicle Earth usually -ve (Sometimes this wire is thicker than the others)
4 Green Permanent power (usually +ve), can be used for internal caravan lights etc.
5 Brown Rarely used
6 Red High drain power (usually +ve)
This only supplies power when the engine is running.(To stop high drain items e.g. Fridges, draining the car battery)
7 Black Second earth connection (usually negative)
8 Pink or Yellow or orange or Other Reversing Light (may affect trailer brakes)
9 Purple or Orange or Green or brown / blue or Other Permanent Power (usually +ve)
10 Grey
or Blue
or Brown and Red
or Other
High Drain Power (usually +ve)
This only supplies power when the engine is running.(To stop high drain items e.g. Fridges, draining the car battery)
11 Clear
or Black / White
or Red
or Blue / White
or Other colour
Another Earth (usually -ve) intended as return wire for pin 10
12 Buff or Blue / White or Brown or Other Rarely used, intended for use within an alarm system or sensor device
13 Black / White or Red / White or Red or White / Green or black / red
or Other
Another Earth (usually -ve) intended as return wire for pin 9

Lorry (24V electrics) ISO-1185 Connector (also known as 24N)

This wiring is sometimes found on lorries with 24V electrics - don't confuse it with the 12V car electrics unless you want a big repair bill!
ConnectorLabelColourDescription
7 pin 24V Lorry ISO-1185 1 White Wire Earth (usually -ve)
2 Black Wire Left hand tail/side lights
3 Yellow Wire Left hand indicators
4 Red Wire Brake lights
5 Green Wire Right hand indicators
6 Brown Wire Right hand tail/side lights
7 Blue Wire TRL control (often unused)

Lorry (24V electrics) ISO-3731 connector (Also known as 24S)

This is used as an accessories socket. There should also be a 7-pin lighting socket (described above)
ConnectorLabelColourDescription
7 pin 24V lorry ISO-3731 1 White Wire Earth (usually -ve)
2 Black Wire ABS Warning System
3 Yellow Wire Reversing lamps and reversing audible warnings
4 Red Wire Permanent power (usually +ve)
5 Green Wire Rarely used
6 Brown Wire Power supply to the ABS system (usually +ve)
7 Blue Wire Rear fog lights
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