On The Road - Towbar Electrics

This information has been placed here to provide a point of reference to anyone who wishes to know what wires do what on their towbar connections.

Cars which are fitted for towing caravans will also be fitted with at least one, if not two electrical connection sockets attached to or adjacent to the tow ball. Commonly known as 12N (road lights) and 12S (fridge and battery) sockets.

More recently European made cars have been fitted with the ISO 11446 13-pin socket which was introduced in 1988, and is our preferred connection standard - especially as a new Eriba caravan will be supplied with an ISO 11446 13 pin plug

The 12N socket (usually black)

This socket deals with power from the vehicles indicators, fog lights and sidelights - transferring that to the caravan lights.

The 12S socket (usually light grey)

The 12S socket takes care of the supplemental power required by the caravans reversing lights, battery charger and fridge. Before 1999 a slightly different wiring standard was applied - most noticeable is that the fridge now has a dedicated "earth" and that the battery feed is shared with the interior lights - caravan relay switches between charging the battery when the engine is running or the interior lights from the car battery when not

13 pin (ISO 11446) socket

The 13 pin (ISO 11446) or Jaeger connector is an international standard (introduced in 1988) and is more common on European towbar electrics. Basically combining the 12N and 12S into one socket, this design is significantly better because:

• Every pin and receptacle is designed to carry 25 amps
• It is water proof when connected
• It is corrosion resistant, the electrical connections are electro-plated and designed to survive European winters
• The coupling mechanism is a positive twist lock
• The coupling socket has built in sensors (micro-switch or the car computer) that automatically detect when the caravan is connected and inform the car computer to turn off devices like reversing sensors, fog lights, and if fitted enable the Trailer Stability Assistance program - TSA (or TSP) - portion of the car ESP system

For some years these have been standard in Europe and a standard offering on all new cars. We've heard reports of some tow-bar centres preferring to fit the 12N+S because they know that system or haven't bought the new 13 pin tester, but we understand that the UK caravan industry will adopt this standard for the 2009 model year.

In all the years of owning ISO 11446 systems, we've never cleaned the pins or had any problems. Which ever you think is best is up to you, but we're all for the 13 pin system.

The pin allocation is set out below, the column labeled "ISO Wire Colour" shows the official ISO 11446 standard and is the colour of the wires in the cable fitted to the Eriba. Whereas the column labeled "Old Wire Colour" shows what may be fitted to your car - the wiring kits should follow the ISO 11446 standard, but they may just follow the 12N+S standards because that cable was used - and you will notice that some colours are repeated in the 12N+S.

Note: We've had reports that car manufacturers (explicityly those that offer a factory fitted tow-bar) fall into two camps - one group that provide a complete wiring harness to the ISO 11446 standard - and another group that only provide wiring for "road lights" as standard and you "need to discuss your requirements" with the car dealer before ordering.

ISO 11446 13 core cable and connectors

Every so often people write to say that they have damaged their caravan cable - unless you support it with a rubber bungee - it's all too easy for the cable to drop and drag on the ground...

Finding the correct grade of replacement 13 core cable hasn't been that easy in the UK - companies like Towsure sell the wrong grade with only 1 heavy duty wire, because a caravan needs five heavy duty wire cores.

However we are pleased to report that Sargent Electrical Services (www.sargentltd.co.uk) do sell the correct grade of cable, and many other electrical components that would be useful in an Eriba project.

Converting

It is possible to get adaptors that convert two sockets on the towbar to a single 13 pin european socket, and vice versa.

These are some examples (click thumbnail to see larger image in a new window) but be warned, some manufacturers adaptors don't provide the fridge power connections

Conversion lead from 12N 7 pin socket plus 12S 7 pin socket to 13 pin Euro Socket. (Converts a vehicle with two 7 pin sockets to a caravan with a 13 pin plug)

Conversion lead from 13 pin Euro socket to 12N 7 pin socket plus 12S 7 pin socket. (Converts a vehicle with a 13 pin socket to caravan with two 7 pin plugs)

Warning: We have reports that some of these adaptors are supplied wired incorrectly - with missing fridge wiring or just simple mistakes

If you are looking to install your own towbar then I was lucky enough to stumble upon this site www.fittinginstructions.co.uk which has a detailed database detailing how to mechanically install several makes of towbar onto most models of car.

Usually when you purchase a kit you will be given all parts required and detailed instructions on how to electrically install it.