7 pin trailer plug 12S (S type Grey Plug)

The 7 Pin ‘S’ Type ( 12S ) trailer plug is used for supplying reverse lights and
gives auxiliary power to other systems such as fridges, internal lights and charging systems

This was replaced in 2008 by the 13 pin Euro plug on all new caravans

The 7 pin ‘N’ type (12N) plug will still be used on O1 class trailers and many towbar fitters
will still offer the 7 pin Socket as the cheapest alternative

It is recommended that a split-charge relay should be wired into your ‘S’ type caravan wiring
At a set voltage this relay will divert some of the power that usually charges
your vehicles battery to the auxiliary systems in your caravan
This is useful for charging auxiliary batteries and powering appliances like fridges and freezers while you are driving.

On the rear of the pins the numbers are marked in the plastic next to each pin

The pins usually have a small screw to retain the wire on the back

When assembling a plug always remember to slide any grommets and caps down the cables before you start to attach cables

The table below this shows the pin numbers in the 7 pin plug, the colour wire that should connect to the pin as the diagram above, and then states the function that the wire should power

Pin No.Wire colourFunction
1.YellowReversing Light
12v ignition on
(battery charging)
3.WhiteEarth for terminal 2 and 4
4.Green12v Permanent Power
(direct from battery)
5.BrownReversing sensors (usually spare)
6.Red12v Ignition On Power (fridge)
7.BlackEarth for terminal 6