Have I blown a fuse?

I don't know your car .... but have you looked in the back of the car where the grey cable enters the boot (assuming saloon) and traced back where the 12S loom connects to the car? There might be an inline fuse there somewhere. Alternatively, there might be a fuse in one the car's fuse boxes if who ever connected the 12S loom used a point that VW had intended for use to supply the caravan.

Thanks MollysMummy.

I can trace approx 1M of cable without removing exterior trim. And no signs of cable around the spare wheel.

If it's likely there's an in line fuse I'm going to dig a bit deeper before getting the professionals in, I think the back of the rear light clusters might be a good place to start.

Although I'm a bit like the guy off the Skittles advert when it comes to cars. 

The area around the back of the lights will probably only supply the black 12N socket .... it's the grey cable you need to follow.

I know you want to use the tow bar fitter (rather than an auto spark) as a last resort, but they might just know where the feeds are on your VW & know where a fuse carrier is likely to be fitted so not even charge you. There will be a fuse somewhere for just the occasion that a cable gets damaged.

Depending on the age of your car the (voltage sensing) split charge relay which provides the fridge/battery charger supply maybe wired direct to the car battery via a fuse. Maybe worth checking near positive battery post for fuse holder.

Thanks Wellmad, 

Have taken MollysMummys advice and asked a very nice man at Robson Caravans , Wolsingham.

Apparently the cable should be wired directly to the alternator.

When I get a minute I'll have a poke about around the battery and alternator then report back.

Taking a feed directly from the alternator close the relay to supply the caravan's fridge & charging is quite an old way of doing things .... as mentioned above, voltage sensitive relays are the way to go. 😉 You need a very nice man at a tow bar fitting place rather than the caravan dealers.  ☺