The electrical connections between car and caravan are made with one or two 7- pin sockets on the rear of the car with appropriate plugs attached to leads on the caravan. In the simplest of arrangements, only one plug and socket to feed all the road lights and flashing indicators need be used. In this case a 12N plug and socket would be used. This is coloured black and has four pins and three contact tubes on the plug (three pins and four tubes on the socket).

If, in addition, power, charging or refrigerator connections are required in the caravan these should be supplied through a 12S plug and socket which is light in colour (usually grey) and the plug has five pins and two contact tubes. In addition the centre pin on the plug is slightly longer than the rest to ensure that the two plugs and sockets are not interchangeable.

When looking at the rear of the car the 12S socket should always be mounted to the left of the 12N although they can be mounted to one side of the towing ball. The diagram on the next page shows the recommended wiring connections.

A refinement not shown on our diagram, and which some caravanner's may find desirable, is to incorporate a switch in the car rear fog lamp circuit after the socket take-off point (or a two-way switch at the take-off point) to cut out the lamps on the car when a caravan is on tow. This is permitted by the regulations and could be an advantage if the car rear fog lamps are mounted high where they could cause glare off the front of the caravan.

The law requires that cars and caravans manufactured on or after October 1, 1979, and first used on or after April 1, 1980, be fitted with at least one rear fog lamp of E marked pattern. In the case of mixed combinations of vehicles it is not necessary to:-

1. In the case of a new car/old trailer to fit rear fog lamps to the trailer
2. In the case of an old car/new trailer to fit rear fog lamps on the car and/or to 6RA relay - Lucas part number 33213. A suitable alternative is Hella relay type 4RA 205 LGE-141 connect the trailer rear fog lamps to the car's electrical circuit.

It is an offence to use rear fog lamps in conditions other than those of fog, snow, heavy rain or spray, smoke or any similar condition.

Pin numbers & colours

12N:

1. left indicator (yellow),
2. rear fog lamps (blue),
3. earth (white),
4. right indicator (green),
5. right rear light and number plate light (brown),
6. brake lights (red),
7. left rear light (black).

12S:

1. reversing lights or reversing catch (yellow),
2. caravan battery charging (blue),
3. earth (white),
4. power from car battery (green),
5. sensing device (brown),
6. refrigerator (red),
7. no allocation (black).

7RA relay - Lucas part number 33335.
A suitable alternative is Hella relay type 4 RAOO3 LXG-141.