Standard 7 pin UK trailer wiring - '12N'

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Number plate light(s) wired to side light(s).

Indicator circuits should have a buzzer or other warning so that the driver knows the trailer indicators are working. This buzzer should buzz or beep-beep or flash in time with the indicators.

Over 1.3m wide, must have rear fog light. Over 1.6m wide, must have front marker lights. Over 6m length, must have side marker lights.

This is motorcycle.co.uk's site, so this is relevant for bike and car trailers in the UK. Not multi-axle caravans, agricultural tree-haulers, Winnebagos, etc... Broadly similar in Europe, may well be very different elsewhere. And there is now a 13-pin 'Euro-Plug', see below.

Some basic regulations...

• Motorways & Dual Carriageways, 60 mph. May not use the outside lane of a 3 or more lane motorway.
• Other roads, 50 mph.
  
  
• You must have a full licence to tow anything. UK licence Category B passed before 1997 - up to 8.25 tonnes car+trailer, after 1997 - up to 3.5 tonnes car+trailer. (Check the full regs at DVLA)
• Trailer over 750Kg gross weight - or over half the weight of the towing vehicle - trailer must have brakes. That's gross weight, which includes the weight of whatever you are carrying on it.
  
  
• The trailer must show the same registration number as the towing vehicle. (It seems to be allowed to use the plate off the back of the vehicle on the trailer, which might be useful for hiring or borrowing....)
• All trailers must have suspension. So motorcycle.co.uk's old solid-axle trailer is illegal then, oh dear.
  
  

For buying and fitting lights and stuff, it is easiest and cheapest to buy a trailer board from your local parts supplier, Halfords or wherever. It will come with all required legal lights and reflectors, ready to bolt on and plug in for somewhere north of a tenner. If you want to make your own, we like Vehicle Wiring Products. Construction and Use regulations apply, you can look them up in various places. But as long as things are positioned sensibly and look like a tidy job, you'll probably be OK.

If you need a number plate, your local parts supply again, but take some ID and your registration document or equivalent, they need proof that you are allowed to use the number. You still sometimes see sticky-backed-plastic yellow plates and black numbers at autojumbles, but its now virtually impossible to get them through even specialist suppliers like Indespension or Pinnell & Bax.

If you want to make the whole trailer, you want your local Indespension supplier or similar.

You won't need this on a bike or car trailer, but while we are here, if you are wiring up for a caravan or similar....

7 pin UK Supplementary Socket wiring - '12S' - pre 1999

7 pin UK Supplementary Socket wiring - '12S' - after 1999

Potential conflict on pin 2 if car wired one way, trailer the other.

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13 pin Euro-Plug

These sockets are not common yet, but if you have to modify your trailer wiring to plug into one....

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