If you plan to tow a caravan, trailer or bike rack, it is essential you use the right electric towbar kit.
Because the towing vehicle's lights are obscured by a caravan or trailer, you are legally obliged to have another set of working indicator and brake lights on what is being towed - making your vehicle and your intentions obvious to other road users.
By law, trailers must have:
- Two red sidelights on rear
- Two red stop lamps
- Illuminated number plate
- Two red, triangular reflectors
- Amber indicators that can flash 60- 120 times per minute (if more than 1.3 metres apart, they must also have at least one red fog lamp)
Towbar wiring kit explained
An electric tow bar wiring kit links the electrical system and the lighting circuit of your car to the lighting panel on the caravan, trailer or bike rack being towed.
Single or twin electrics: Which should I use?
Three types of towbar electric plugs are used on UK roads. These are single 7-pin electrics, single 13-pin electrics, and twin electrics.
As the name suggests, single 7- and 13-pin plugs use one plug, while twin electrics use two 7-pin plugs (often required with older caravans or trailers).
12N and 12S explained
12N electrical systems provide brake, indicator and fog lights over a 7-pin plug.
These are the 'must-have' lights on whatever is being towed.
12N electric, meanwhile, can afford 'advanced' or 'supplementary' electrics - including reverse lights, and power for a caravan’s interior (fridge, lights etc) - via an extra 7-pin twin electric plug system.
Newer vehicles harness 13-pin plugs that deliver both 12N and 12S capabilities through a single plug.
Do all systems have the same socket types?
No. There are two socket types for towbar electrics. The one you need will depend on the vehicle you are driving/towing.
Adapters are available if the towing vehicle and caravan/trailer have differing sockets (see below).
7-pin towbar wiring explained
As mentioned, 7-pin electrics provide the legal minimum lighting system - tail lights, brake lights and indicators.
What if I have a towbar-mounted bike rack that obscures my vehicle's lights?
Essential lights must be visible to other road users, so if these are obscured you will need to install a lighting board on the bike rack.
Are 7-pin electrics enough?
If you only need the basic lighting functions - for instance with a smaller trailer - then 7-pin electrics should suffice.
For example, trailer stability control may not be needed.
13-pin towing socket explained
The 13-pin system amalgamates the essential lights with supplementary lights through a single plug, making it neater and easier to use all these light functions.
Each pin connects to a colour-coded wire - each of which performs a particular function. For example, yellow (1) is the left hand indicator, blue (2) is for fog lights, white (3) is earth, and green (4) is the right hand indicator.
13-pin systems connect the electrics of the towing vehicle to things like the caravan’s fridge and interior lights, and the stability control system.
Which towbar wiring kit do I need?
There are two kit types available. The one you choose will depend on how old your vehicle/caravan is.
The best option is to buy a kit specially designed for your vehicle - thereby eliminating the possibility of invalidating your warranty.
A dedicated towbar wiring kit may also warn you if the lights on the trailer or caravan fail.
Should I use a universal wiring kit?
Universal wiring kits are quick and cheap to fit, providing all the basic components needed for your towing lights.
That said, functionality is much more limited with a universal wiring kit - and you would risk your warranty becoming invalid since it does not meet the requirements set out by the manufacturer.
What is a towbar wiring bypass relay?
If you have a newer vehicle with complicated electrics, you'll need to fit a towbar wiring bypass relay.
A towbar wiring bypass relay stops too much power being drawn from the towing vehicle's battery.
It isolates the power supply, preventing the universal wiring kit from causing blown fuses, dim lights or simply a cut in the power supply.
The relay sends an electrical pulse when a function (e.g. the brake pedal) is used, rather than permitting a constant supply of power. This protects the battery from any potential faults in the caravan’s towing electrics.
It's best to have your towbar electrics installed by an experienced professional.
Will I need a towbar electric adapter?
An adapter is required if the towing vehicle and caravan/trailer have different plugs. For example, if your towbar has 7-pin electrics but your caravan has 13-pin electrics, a 7-pin-to-13-pin adapter is needed. Conversely, a 13-pin-to-7-pin adapter would be necessary.
Naturally, in either case, you would only get the functionality of the 7-pin system (the additional pins being redundant).
