ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades 12N/12S Vehicle & Trailer wiring

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).]

On the continent you'd use a standard 13 poles outlet for that sort of trailer, wouldn't you?

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).]

Paul,
As far as trailer connectors go in NZ, we have 2 options, round or flat, as shown below:



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.

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

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:



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..... )



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

Alan,


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.

My Skodas' (thats right - we've got two! ) 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).]

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

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.

Paul,

Here is a picture of the pin layout (and wiring colour coding) of the plug (male):



Pin designations are as follows:

• 1 - Left Hand Turn (Yellow)
• 2 - Reverse (Black)
• 3 - Earth (White)
• 4 - Right Hand Turn (Green)
• 5 - Service Brakes (Blue)
• 6 - Brake Lights (Red)
• 7 - Tail Lights (Brown)

[This message has been edited by Trumpy (edited 08-01-2006).]

Hmm... The pin numbering on your flat connector seems to correspond closely to that of the 12N standard here, with reverse in place of fog light and an electric brake line in place of one of the tail-light feeds.

Do the same pin numbers apply to the New Zealand 12N-style round connector?


Funnily enough, I think it was on a Skoda that my mother had when I was a kid which first brought the arrangement to my attention. (Signal, stop at the curb, signal switch doesn't cancel, switch off, get out, and then wonder why half the parking/tail lights are on.)


Just in case any of our European readers are not aware of the differences, let's explain that it is still normal in North America for vehicles to use combined red turn/brake lights.

I'm not sure about other countries, but here in the U.K. all new vehicles built for the British market have had separate amber turn signals on the rear since the mid 1960s, hence the separate left turn/right turn/brake connections on the 12N connector.

In the U.S. & Canada you can buy a converter unit so that a car with independent amber signals can be connected to a trailer (which will have the standard combined red brake/turn lights).


I know that the 7-pin Bargman-style connector is becoming pretty much the standard over there now, but how common are the 5- and 6-way round connectors?
http://www.horsetrailerworld.com/home/wiring.asp

Any idea when these various formats were introduced?

By the way, it seems from Mike's post that New Zealand also has electric trailer brakes, but you won't find them here on regular utility trailers and caravans (travel/camping trailers). Inertia/surge brakes with a direct mechanical linkage from the towing hitch to the brakes is the norm here (except for the smallest trailers with no brakes).



[This message has been edited by pauluk (edited 08-01-2006).]

I don't know, athough the Bargman type connector is mostly used on the fifth-wheel and goosneck type trailers, and the 4 pins or 6 pin round (which a couple of our trucks have installed), with ball hitch trailers.

Fifth-wheel trailers are quite rare over here. Almost all utility and camping trailers these days use a 2-inch ball hitch.

The turn signal switch turning on one side of the "parking lights" with the ignition off was for parking in an unlit area. Think it was a German requirement in the 60's/70's. It may have also lit a small bulb in the headlight on the selected side.

Ah, that sounds quite plausible. I suppose that also ties in with the specification for the 12N connector which says that the right-hand tail circuit should also feed the license plate light. That way when parking on the right at night, one could leave the left-hand lights on without the plate light adding to the current drain.

The arrangement would be completely useless in Britain. If parking in a place which requires lights, we need to leave all the parking/tail lights on, not half of them!


On many European cars a small bulb set in the side of the headlamp reflector is the front parking light.

British cars have used several configurations of front lights in the past:

1. Combined parking light & turn signal with dual-filament bulb (equiv. to #1157) behind a white lens, just like the standard pre-1963 American arrangement (although on some vehicles the parking lights remained on when the headlights were switched on, as with all post-1968 U.S. vehicles).

2. Separate white parking lights and amber turn signals, each with its own bulb (either in two entirely separate assemblies or a double cluster but still effectively separate).

3. Parking light incorporated into the headlight, and a separate amber turn signal.

Configuration #1 went out of use from 1965 when cars had to be fitted with amber signals but were still required to have white parking lights (thus ruling out modern U.S.-style combined amber park/turn lights for U.K. market cars).

While there are still some cars using method #2, they're becoming less usual, and method #3 is pretty much the norm on most new vehicles now.

While we're on the subject, a few other U.S. vs. U.K. vehicle lighting differences amber/red side marker lights and reflectors are not required on regular cars here and are not normally fitted. Larger trucks, buses etc. are required to have clearance lights on the upper corners, but don't have to be fitted with the three width ID lights in the center.

Also, in British parlance, you might hear the term "side lights." That doesn't refer to side marker lights, but is actually the more usual colloquial name here for the front parking lights. (In government-speak they're called "front position lamps.")

All in all, the different configuration means that those of us who drive U.S. vehicles here tend to "stand out from the crowd" a little with our different lights.