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#145862 - 07/29/06 11:26 AM 12N/12S Vehicle & Trailer wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I don't know how many other people here ever get involved with caravan/trailer wiring, but I'm sure we must have some.

Is it just me, or do the conductors in the standard black 12N trailer cable seem to be getting very thin these days? The common return (white) is reaching the point at which voltage drop is really noticeable.

I've taken to running the heavier 12S-type cable in place of 12N whenever possible to get some larger gauge wire and less voltage drop.

Note: For those not familiar with the U.K. system, we generally use two 7-pin connectors: 12N (black) for the road lights and 12S (white or gray) for the supplementary functions - trailer battery charge, fridge, etc.


[This message has been edited by pauluk (edited 07-29-2006).]


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#145863 - 07/29/06 06:16 PM Re: 12N/12S Vehicle & Trailer wiring  
Wolfgang  Offline
Member
Joined: Sep 2005
Posts: 153
the very West of Germany
On the continent you'd use a standard 13 poles outlet for that sort of trailer, wouldn't you?


#145864 - 07/30/06 06:17 AM Re: 12N/12S Vehicle & Trailer wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Wolfgang,

How common are the 13-way plugs there now compared to the separate 12N/12S 7-way connectors?

The 13-way types are available in the U.K. now, but are still comparatively rare. They are also much more expensive, e.g.

12N/12S 7-way plugs & sockets, less than £2 each.

13-way types, plug £7.75, socket £10.75

From http://www.towsure.com/default.asp?t=6459

[This message has been edited by pauluk (edited 07-30-2006).]


#145865 - 07/30/06 05:51 PM Re: 12N/12S Vehicle & Trailer wiring  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,223
SI,New Zealand
Paul,
As far as trailer connectors go in NZ, we have 2 options, round or flat, as shown below:

[Linked Image]

There is no standard here, especially at hire firms, chances are, if you hire a trailer the plug on the trailer will be the opposite of the socket that is on your car. [Linked Image] [Linked Image]


#145866 - 07/31/06 03:15 AM Re: 12N/12S Vehicle & Trailer wiring  
Alan Belson  Offline
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Paul, I just renovated our old 1-ton trailer electrics. The new lights, cable and plug are utter rubbish. Thin horrid plastic moldings, no attempt made at keeping the guts dry. Cheap, thin pressed tinplate receps and the worst bulbs I ever saw- I actually dented the bayonet caps trying to fit them! As you say the conductors were a mite small. So thin, in fact, that I had a job getting the stupid nasty Chinese screws to bite to get any contact and wound up with the soldering iron. I threw the new plug and the supplied bulbs in the bin. Surely we can't be condemned to accepting all this ghastly imported crap for ever can we?

But on the bright side, the packaging was superb! Took a pair of tinsnips to open the bubblepack!

Alan


Wood work but can't!

#145867 - 07/31/06 07:25 AM Re: 12N/12S Vehicle & Trailer wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Mike,

Your 7-way flat connector is unfamiliar to me, but the round type appears to be exactly the same as our "12N." Do you know the pinout arrangement?

We used to have a 5-way round connector at one time for basic trailer lighting (tail, left turn, right turn, brake lights, ground), until it was replaced by the 12N arrangement in -- I think -- the late 1960s/early 1970s.

Here are our connections/color code for 12N:

[Linked Image]

1. Yellow = Left turn signal
2. Blue = Rear fog light
3. White = Common return
4. Green = Right turn signal
5. Brown = Right-hand tail light
6. Red = Brake lights
7. Black = Left-hand tail light

Pin 2 was originally spare or used as a permanent 12-volt feed for caravan interior lights etc. Then in 1980 the "powers that be" dictated that all new vehicles had to be fitted with a rear fog lamp, so it was reallocated for that.

The split left/right tail light feeds are apparently part of the European standard, as European cars fuse them separately. (Many European cars also have a curious arrangement whereby when the ignition is off the turn signal switch allows you to illuminate the tail/parking lights on just one side of the vehicle only. Maybe Wolfgang can elaborate on that.)

The 12S connector is similar to the 12N but has the male/female on the center pin reversed (and, as mentioned, the standard 12S cable is heavier gauge). The 12S standard was as follows:

1. Yellow = Reversing light/surge-brake solenoid
2. Blue = Battery charge
3. White = Common return
4. Green = Permanent 12-volt feed
5. Brown = Sensing device
6. Red = Refrigerator
7. Black = Spare

Pin 2 is wired through a relay so that it is powered only when the engine is running and the generator producing output (ditto pin 6).

Pin 5 is allocated for a remote sensing device on the caravan/trailer, but in practice is normally unused.

The 12S standard was revised slightly in 1999. First, it was decided to provide a separate return path for the fridge power on pin 7 (black). Second, the newer electronic caravan charge units now don't rely on the switched power on pin 2 for charging, but instead just take power from the permanent feed on pin 4 and connect automatically when the appropriate increase in voltage is detected.

That means that pin 2 is no longer needed for battery charge, which is fine. Unfortunately, some dimwit in the standards committee (presumably) decided that pin 2 should be re-assigned to the function of indicating to modern car electronics when a trailer is connected. And how does it do that? By having the trailer wiring ground pin 2!

So, post-1999 caravan + pre-1999 12S car wiring = Blown fuses!

(Or judging by the number of horrible lash-ups I've seen in cars where the charge relay is connected straight to the battery positive with no fuses..... [Linked Image] )



[This message has been edited by pauluk (edited 07-31-2006).]


#145868 - 07/31/06 07:30 AM Re: 12N/12S Vehicle & Trailer wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Alan,

Quote
Thin horrid plastic moldings, no attempt made at keeping the guts dry. Cheap, thin pressed tinplate receps and the worst bulbs I ever saw- I actually dented the bayonet caps trying to fit them!


I know exactly what you mean. Some of those "el cheapo" trailer lights are complete junk.

I've seen some which even from new seem to produce very dodgy connections to the bulbs. Give them a few months of English winter, and it's not surprising the number of trailers we see driving around with dim/flickering/non-functioning lights. [Linked Image]


#145869 - 07/31/06 01:22 PM Re: 12N/12S Vehicle & Trailer wiring  
Hutch  Offline
Member
Joined: May 2002
Posts: 381
South Oxfordshire, UK
Quote
The split left/right tail light feeds are apparently part of the European standard, as European cars fuse them separately. (Many European cars also have a curious arrangement whereby when the ignition is off the turn signal switch allows you to illuminate the tail/parking lights on just one side of the vehicle only.


My Skodas' (thats right - we've got two! [Linked Image] ) do that here in the UK Paul. I only notice when I turn the car off with the indicator still turned. The car squalks when you open the door because a tail light is now on!


[This message has been edited by Hutch (edited 07-31-2006).]


#145870 - 07/31/06 05:51 PM Re: 12N/12S Vehicle & Trailer wiring  
Alan Belson  Offline
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
I just went out and checked earlier. My Opel does it, well I never! Why on earth would you want half a set of lights for heaven's sake!!?

Hutch. I take it these are modern Skodas, [VW inspired], and not the delightful command economy ones where one crawled past a police officer in a cloud of soot and shouted "VAROOOOM!! out of the driver's window hoping in vain to get that 'impossible' speeding ticket?

Alan


Wood work but can't!

#145871 - 07/31/06 06:56 PM Re: 12N/12S Vehicle & Trailer wiring  
classicsat  Offline
Member
Joined: Nov 2002
Posts: 456
I get involved in two or three trailers a year.

Here, non braked or intertia braked trailers use a simple 4 pole flat plug, with Ground (white, male prong), Tail (brown), Yellow (Left Stop/Turn), Green (Right Stop/Turn)

Electric braked trailers use a 7 pin round connector (which uses flat pins), and adds continuous power, Brake (controlled from an electronic brake controller added to the tow vehicle), and an auxillary line.

Air braked trailers use yet another 7 pin standard, with separate circuits for clearance and tail lights.


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