MOT 13pin towbar electrics

Ibrahim5

Got my first MOT with 13 pin towbar electrics which are checked during the MOT. I have an adaptor which converts it to 12N and 12S. Some people say leave the adaptor on and then they aren't allowed to check them. Everything works OK but if leaving an adaptor on avoids all problems then it may be worth it?

Grumpy_chap

If the electrics are faulty, surely you'd want to know so you can fix it and be safe when towing.

Ibrahim5

I have said they are OK. There are reports of MOT testers saying they are faulty when they aren't.

facade

Just leave the adapter on, the tester should interpret "test as presented" to mean visual only as it is a 7 pin.

There is nothing in the MOT regs to say they can't unplug the adaptor though, only that they don't need to test if tools are required to access the socket.

Section 4.10

https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/4-lamps-reflectors-and-electrical-equipment

It does say to ignore the odd led indications that the approved tester gives with a canbus car- which seems to be their "fix" for the problem that has been continually reported since 2014 I believe

(For the interested, the tester has to use one of only a few "officially approved test boxes" some of which don't work properly and show faults where there are none, or don't register as a trailer with the car electrics so it doesn't energise the socket. There is no problem with a trailer board with bulbs in, or canbus compatible leds. This has been going on for years)

chrisw

I never even realised that a trailer socket is now part of the MOT. I can see why they've done it but a dangerous failure for a non working socket seems rather excessive.

Herzlos

chrisw said:

I never even realised that a trailer socket is now part of the MOT. I can see why they've done it but a dangerous failure for a non working socket seems rather excessive.

It's only for the newer 13 pin ones and to be fair it's an extension to the light system so you'd need to treat it the same as if any of the car lights don't work.
I think they need to assume that if a car has a towball fitted that they tow something that will obscure the on-board lights.

It still won't do anything for faults with the trailer, but it's at least a start.

tedted

the seven pin is also looked at for security etc but not electrically tested

badger63

Just failed the mot on towbar electrics..they say nearside position lamp not working but it is!!! Said I would tow my caravan down and prove it and they said it's not a sanctioned test and would still fail arrrgh

Mildly_Miffed

chrisw said:

I never even realised that a trailer socket is now part of the MOT. I can see why they've done it but a dangerous failure for a non working socket seems rather excessive.

Right up until somebody plugs a trailer into it, and gets no lights at all...

https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/4-lamps-reflectors-and-electrical-equipment#section-4-10

As for "they fail them when they're working!" - no, they can't and won't do that. They have to use an approved socket tester, not just some ropy old light bar that's kicking around...
https://www.prosol.co.uk/product/13-pin-towbar-trailer-socket-tester-dvsa-approved-for-mot-use/
If the towing electrics don't work on that, then how is that "but it works!"?

Mildly_Miffed

badger63 said:

Just failed the mot on towbar electrics..they say nearside position lamp not working but it is!!! Said I would tow my caravan down and prove it and they said it's not a sanctioned test and would still fail arrrgh

Probably miswired, so that both are being fed through the OS circuit.

Herzlos

Ibrahim5 said:

Got my first MOT with 13 pin towbar electrics which are checked during the MOT. I have an adaptor which converts it to 12N and 12S. Some people say leave the adaptor on and then they aren't allowed to check them. Everything works OK but if leaving an adaptor on avoids all problems then it may be worth it?

You're going to drive it to an MOT with adapter cables hanging from it? Whilst I'm not sure that'd be a fail in itself unless they were hitting the ground, that's going to attract a bit of suspicion.
I'm assuming most people leave the adapter on the caravan side.

If it works, then you shouldn't have a problem anyway, and if it doesn't, you're better off knowing.