7 Pin to 13 Pin Electrics

So I've ordered myself a shiny new trailer. Given that I've got 13 pin electrics on my Amarok, I was planning to change the connector on my P38 to a new Euro plug to avoid messing around with adaptors. I only have 12-N plug on Range Rover currently. I know I can swap this for a 13 pin, and will have the road lights operational (but not reverse light).

Question is: do I need to hook up the reverse light to my new 13 pin plug for the Rangey to pass MOT? As I understand, 13 pin electrics are part of the MOT test, whereas they just used to check your 12-N/12-S plugs were secure?

Rather than change the 12N plug for a 13-pin, I'd add the 13-pin while leaving the 12N in place. The two plugs will fit side-by-side in the same way as 12N+12S, and gives you the option to tow any trailer, whatever electrics it's fitted with. The 13-pin can be simply wired up in parallel with the 12N.

As for the reverse light feed, it makes sense to do the job properly and wire it in

FlyingPete said:

Rather than change the 12N plug for a 13-pin, I'd add the 13-pin while leaving the 12N in place. The two plugs will fit side-by-side in the same way as 12N+12S, and gives you the option to tow any trailer, whatever electrics it's fitted with. The 13-pin can be simply wired up in parallel with the 12N.

As for the reverse light feed, it makes sense to do the job properly and wire it in

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Agree with what you are saying but some versions of the 13 socket have a switch built in that disables the towing vehicle rear fog lights when you couple up (I fitted one to my 300 TDI Def), there are other versions that don't have the switch but use the vehicle electronics to detect that a trailer is connected and then disables the fog lights. Not sure what level of sophistication the P38 has but I'd guess that with 12N/12S already fitted it probably won't have the electronics to support automatic detection and you will need to use the 'switched' 13 socket. That makes things slightly more complex than just wiring in parallel but isn't a show stopper.

Kwakerman said:

Agree with what you are saying but some versions of the 13 socket have a switch built in that disables the towing vehicle rear fog lights when you couple up (I fitted one to my 300 TDI Def), there are other versions that don't have the switch but use the vehicle electronics to detect that a trailer is connected and then disables the fog lights

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All you'd be doing is wiring the 12N pins in parallel with pins 1-7 on the 13-pin. If the 12N socket has no fog light cutout switch, then the fog light may not be switched off if you connect a trailer up via the 12N. But with something plugged into the 13-pin, it should still operate correctly.

The 12S plug does have the facility for trailer detection via pin 5, but this is seldom used. Likewise the 13-pin at one point had pin 12 allocated to trailer detection (but currently it's not assigned to anything). If you wanted to use this feature, you'd link pin 12 (or pin 5 on a 12S) to any ground pin in the plug. The pin in the socket can then go to a relay which will break the circuit to the fog light.

I've looked and can't find anything that says that disabling the towing vehicle's rear fog lights is a legal requirement, so it seems that it's just an owner's personal preference in an attempt to reduce reflected glare. In which case there would appear to be no problem with simply wiring the 13 pin socket in parallel with the 12N socket as @FlyingPete says, of course with due attention paid to the gauge of wire and the security of the connections.
Where an owner has purchased a 13 pin socket with a mechanical switch included then by all means wire in a relay to cut off the towing vehicle's rear fog lights, but this modification would only apply to that towing vehicle and not to the trailer. But even if a switch is provided, there seems to be no actual requirement to use it.
Some trailers, even today do not have reversing lights fitted as standard, however since the 13 pin socket has a position alocated to that circuit it's reasonable to assume that it would be tested under the MoT rules for such trailer sockets so I would expect that the reversing lights circuit would be properly wired in.

http://www.caravanclub.co.uk/media/1022790/towbar-wiring-mo.pdf

Thanks all. I hadn't thought of keeping the 712N and putting the 13 pin plug alongside. That seems a fairly sensible approach, and wiring in the reverse light shouldn't be too much of a hassle. Job for one of the weekends fairly soon, I think.

Just thought- the reversing lights on the car are not tested as part of the MOT test- whether they're present, working or broken is completely irrelevant as far as the test is concerned. I'd imagine therefore that the reverse light pin on the 13-pin plug is the same.

I'd still wire it up though, for the sake of doing a good job

FlyingPete said:

All you'd be doing is wiring the 12N pins in parallel with pins 1-7 on the 13-pin. If the 12N socket has no fog light cutout switch, then the fog light may not be switched off if you connect a trailer up via the 12N. But with something plugged into the 13-pin, it should still operate correctly.

The 12S plug does have the facility for trailer detection via pin 5, but this is seldom used. Likewise the 13-pin at one point had pin 12 allocated to trailer detection (but currently it's not assigned to anything). If you wanted to use this feature, you'd link pin 12 (or pin 5 on a 12S) to any ground pin in the plug. The pin in the socket can then go to a relay which will break the circuit to the fog light.

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Found this website, don't know if it is the latest test criteria. Doesn't mention that the fog light cut-off should work on the vehicle but if the correct function of a 13 pin socket is to cut the car fog lights when the plug is fitted then the 'wired correctly to operate the trailer' statement for the 13 pin means could be read to mean that the car lights could go out? One way to find out is for the OP to do it and take it for an MOT, if it fails it is a quick job to remove it for re-test. When I did mine I wired the switch to control the fog light so it wasn't an issue for me.

Kwakerman said:

Found this website, don't know if it is the latest test criteria. Doesn't mention that the fog light cut-off should work on the vehicle but if the correct function of a 13 pin socket is to cut the car fog lights when the plug is fitted then the 'wired correctly to operate the trailer' statement for the 13 pin means could be read to mean that the car lights could go out? One way to find out is for the OP to do it and take it for an MOT, if it fails it is a quick job to remove it for re-test. When I did mine I wired the switch to control the fog light so it wasn't an issue for me.
View attachment 109250

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That would be great fun for sockets wired differently.

There is a way to wire trailer plugs to knobble the towing vehicles.

Endeleus said:

So I've ordered myself a shiny new trailer. Given that I've got 13 pin electrics on my Amarok, I was planning to change the connector on my P38 to a new Euro plug to avoid messing around with adaptors. I only have 12-N plug on Range Rover currently. I know I can swap this for a 13 pin, and will have the road lights operational (but not reverse light).

Question is: do I need to hook up the reverse light to my new 13 pin plug for the Rangey to pass MOT? As I understand, 13 pin electrics are part of the MOT test, whereas they just used to check your 12-N/12-S plugs were secure?

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I've had 13 pin electrics fitted to three different vehicles and never have they been tested for MOT, but never understood why you would not have a reverse light on a trailer or caravan, let other road users and pedestrians know what you are doing

John03 said:

I've had 13 pin electrics fitted to three different vehicles and never have they been tested for MOT, but never understood why you would not have a reverse light on a trailer or caravan, let other road users and pedestrians know what you are doing

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In 'the old days' when there was only the 12N Plug / socket you only had 7 contacts in the plug, that isn't enough to be able to have a reverse light once the 'normal' lights had been wired up (indicators / side / brake & number plate lights etc)

Kwakerman said:

In 'the old days' when there was only the 12N Plug / socket you only had 7 contacts in the plug, that isn't enough to be able to have a reverse light once the 'normal' lights had been wired up (indicators / side / brake & number plate lights etc)

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I knew that just never understood why, but thats also the reason why I switched to the 13 pin plug, and the spare pin I use to connect a camera I have fitted to the back of my caravan handy not only for reversing but keeping an eye of idiots that like to drive close to the rear of the caravan were i cant see them in my wing mirrors

Why not just buy an adaptor? Also, reverse lights on cars are not to inform other road users what you're doing, just simply to illuminate your path which is why they aren't part of the MOT.

Discokids said:

Why not just buy an adaptor? Also, reverse lights on cars are not to inform other road users what you're doing, just simply to illuminate your path which is why they aren't part of the MOT.

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really? then why did my VW fail an MOT test coz one of the reverse bulb had blown, replaced retested then passed?

John03 said:

really? then why did my VW fail an MOT test coz one of the reverse bulb had blown, replaced retested then passed?

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Because the tester was knob, reversing lamps are not part of the MOT test.

wammers said:

Because the tester was knob, reversing lamps are not part of the MOT test.

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+1

John03 said:

really? then why did my VW fail an MOT test coz one of the reverse bulb had blown, replaced retested then passed?

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I'd be asking the guy that does the MOT.