Unit 1-4, Block L, Grants Road,
Greenogue Business Park
Rathcoole, Dublin D24PP28
Tel: 01 497 5713
Towbars & Towing Electrics - Specialist Fitting Service
Cars, Vans & Light Commercial Vehicles

Wiring Diagrams

12N Standard Socket

12N electrical kits (socket with black cover) are used for operating the standard lights on the rear of trailers etc. Some newer vehicles with multiplex wiring may need the addition of a bypass relay kit (see Relay section for more information).

12S Caravan Socket

12S electrical kits (socket with grey cover) are used predominantly for operating internal appliances within a touring caravan, i.e. running of caravan 12 volt fridge, charging leisure battery and offering a permanently live 12 volt feed into the caravan. A split charge relay would also be installed into the tow vehicle to protect the vehicle battery from running down (see Relay section for more information).

13 Pin Socket

This is the continental style electrical connection. Both 12N and 12S electrics are contained within the socket which has 13 pins rather than 7.

This socket is used in mainland Europe and from 2008 all caravans manufactured in Europe will be wired up with 13 pin plugs. It will also become standard in the UK and Ireland over the next couple of years on new trailers, caravans etc.

You can use this socket with UK 7 pin plugs which are on all UK trailers and caravans but you need to use a converter which will split the 13 pin electrics down to two 7 pin sockets or one 7 pin socket depending on what you are towing.

If you wish to operate internal appliances within a touring caravan, i.e. running of caravan 12 volt fridge or charging leisure battery then a split charge relay would also be installed into the tow vehicle to protect the vehicle battery from running down (see Relay section for more information).

Universal By-Pass Relay

Bypass relays are fitted to stop the vehicles light check control system putting a warning light onto the dashboard to suggest that one or more bulbs has blown when actually the trailer lights are taking away a small amount of electrical current.

Bypass relays are also used when wiring onto CANBUS systems to prevent any electronic component failure.

Universal bypass relays do not interact with TSP or cut the reverse sensors out.

Many cars send complex or modulated power signals to switch their rear lights, so making the towing relay work correctly is not simple. The smart bypass relay has a controller that measures the signals from the vehicle's lighting systems against exact criteria to determine which trailer lights should be switched on.

It gets the switching right every time. No chatter, no dim lights, just on and off as they should be. The following two examples are common in cars.

a. When the car uses a modulated power feed to make one single filament bulb perform the function of different lamps (e.g. brake and tail) the relay interprets the modulated signals and switches on the correct trailer lamps.

b. When the car "swaps" bulbs in the event of a bulb failure, the relay again interprets correctly and keeps the correct trailer lights on.

Added Value:

  • Monitors the trailer flashers, with both a built-in audible output and terminal outputs for a remote sounder or warning lamp.
  • Totally transparent: the car does not detect it. It will not cause bulb-failure warnings.
  • Fully snubbed against "spikes" and other hazards
  • Protected: stands rough treatment, accidental current reversals, etc.
  • Future-proof: new in-vehicle scenarios will be accommodated rapidly.
  • Works on every car, complex or not.

Caravan Split Charge Relay

Protecting the Vehicle Battery

When a vehicle tows a caravan and the caravan is equipped with a 12 volt fridge or an auxiliary battery or both, it is necessary to provide a connection between the caravan and the towing vehicle to provide power to these.

When such a connection is provided it is advisable to protect the vehicle's own battery from being accidentally drained by the caravan fridge and auxiliary battery.

The usual way of providing this protection is to install a suitable relay or pair of relays which will turn off the connections when the vehicle's alternator is not running.

Such relays, often referred to as "split charging" or "combination" or "Combi" relays, are normally switched by a connection to the alternator or to some suitable ignition-switched source.

It is absolutely essential that any such relay system should work reliably, fail safe, offer full protection to the battery, and, if possible, to the auxiliary battery.

The self-switching combination relay from Ryder Towing make the installation of these relays much easier and safer, especially in the context of the complex electronics in modern vehicles, and meet all the essential criteria described above.

These devices do away with the need to find a signal current from the alternator or ignition to switch the relays.

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