Tow bar electrics

[Ferrodo]

Hi all,
I have three 15amp fuses at the car battery feeding the tow bar socket. Now I know that one will be the permanent live (ATC) and one will be the switched live (leisure battery charging etc) but for the life of me I can’t see what the third is for.
I have read that it’s for the trailer lights but that can’t be right?
Everything works as is should and the tow bar wiring is a proper dedicated item professionally fitted.
Best regards
R

 

[Gozza2]

Could be for the caravan fridge? If you've got a 13 pin socket, all switched 12v goes through pin 13, but if you've got 2 x 7 pin (or your car has had it in the past), battery charging goes through pin 2 and fridge through pin 6 (on the grey socket) so they may have been wired separately.

 

[Ferrodo]

Hi Gozza
Ta for the reply. Pin 10 is switched and 9 is permanent so all good there. Obviously I have a 13 pin socket
Regards

 

[littlebasher]

The third wire may be a power supply to the split charge relay for your fridge supply - probably the smallest gauge wire

 

[Ferrodo]

That sounds reasonable littlebasher. I shall find which two fuses are linked to pin 9 via the VSR.
I will let you know.

 

[Hutch]

I suppose you could hook up the caravan, and then remove each fuse in turn, and see what does NOT work.
What's your tow car ?

 

[Ferrodo]

2016 Shogun. I think it’s likely that the one fuse is a feed to power the VSR and the other is the feed for the fridge which is switched through the VSR. A bit belt and braces really but the safer way I would think. I will play around with my multi meter tomorrow and pull fuses and see what happens. The triple fuse box plugs directly into the cars main harness so it’s definitely a pukka job. Watch this space

 

[Ferrodo]

So it seems that pin9 is the permanent feed as it should be and pulling the fuse confirms this. Pin 10 (switched feed) has two fuses. Pulling them both no power putting one back in restores power no matter which fuse is in. Any ideas why??

 

[Mr Plodd]

To ensure there is not too much of a voltage drop to feed hee fridge whilst under way would be my guess.

 

[Ferrodo]

Yep I think you’re right Mr Plodd. Can’t see any alternative really. But I would have thought one heavy gauge wire instead of two smaller ones would have been more logical. Strange people these electrical types. Still it all works so I won’t be buggering about with it. Thanks to all for your input
Best regards
R

 

[Buckman]

We have not bothered with having the fridge feed connected as we have never used it in the past even when travelling across to the continent.

 

[Ferrodo]

Yes Mr Buckman we do exactly the same as you. Good quality cool box with a couple of ice packs every time. But if it’s there it has to work and I have to understand how it works. The curse of being being an old retired engineer. 🤭