Audi electrics

There's a bit more to it than just 2 wires but £350 to add the extra wiring is taking the proverbial. I hope you plan on taking your car elsewhere than Audi to get it sorted. A few years back I bought a car with just a 12N socket ie lighting only & paid a local tow bar place £100 to convert to 13 pin including the extra wiring ie the wiring that your are  missing.

A couple of wires and relays don’t add up to £350 - even if a technician does have to re-programme. (That’s where the cost is!) Have a word with a local towbar fitter 👍

Even having the wiring altered won't help with your fridge. See other threads re this problem. Modern ECU's are the problem. I've had 2 new German SUV's since 2012 and neither will run the fridge, even with correct factory electrics.

You also need to be aware that having the electrics changed by other than an Audi dealer "could" invalidate your warranty.

My German SUV's factory wiring powers my fridge ok ... 14 plate so not new, but new enough for me.

I would like to see Audi, or anyone else, knock your warranty claim back if it was completely unrelated to the tow bar wiring.

Which make / model? Be interested to know. BMW X5 and Porsche Cayenne in my case, both with factory fitted 13 pin plugs, but no charge to fridge. It all depends on  the ECU fitted.

BMW a 2012, and Porsche a 2016. Previous to that I had a 2008 Merc 320D with aftermarket towbar and elecrtics, and fridge was fine.

Regarding warranty, if anyone messes with the ECU that is your problem. 

14 plate Merc ML350, factory swivel tow bar 😉

We have a VW 66 plate, we had it fitted with towbar and full 13 pin electrics at a towbar specialist.  Although there is power to all the correct pins, I was never convinced it was charging the battery properly, probably not doing much for the fridge either, but as it is always precooled and is well insulated, that was not a big problem.

After a couple of years, to get the van battery properly charged, essential for powering the mover, I fitted a Sterling "battery to battery" charger in the van.  This is set to automatically charge the battery and then run the fridge every so often, with priority being given to the battery.

These newer cars are just trying to be too clever.

A major problem which not many designers and installer appreciate or understand is volts drop. Cable is often rated for its current carrying capacity, volts drop is never mentioned because it has to be calculated. It is voltage lost as a result of the resistance of the cable and its total length, the current. The lower the voltage you start with, the greater the problem becomes. 

A 20amp cable is quite adequate to charge a battery, or run a fridge, if not too long, but if that cable has to run the length of the car, via a plug and socket, then much of the length of the caravan there will be appreciable voltage lost along the route. Which means your fridge may not receive enough voltage to work as well as it could and your leisure battery could take much longer than it  would otherwise, to reach a full charge on the move.

To get around the problem, I ran 2x 4mm from my car's fuse for the purpose under the bonnet, all the way to the split charge relay at the back, where it splits into battery and fridge feeds. Installers tend to use a single 2.5mm, if you are lucky, or maybe a 1.5mm. 

Measured volts at either my fridge or leisure battery is just a fraction of a volt down on that at my car's battery and both work very effectively.  Adequate voltage at the leisure battery, is absolutely critical to be able to put a sensible charge into it.

Agree.  The B2B charger takes the available voltage and boosts it to the voltage required to properly charge the caravan battery and run the fridge.

I know the cables from the plug to the fusebox in  the van are heavy enough as I fitted them myself when I changed it to 13 pin electrics.  We did not have a charging problem with our previous car (2007 model).

The main problem I had now was that the so called "smart alternator" only charges the car battery to about 70% and ignores the fact there is a caravan battery to charge too.

We need a full battery on arrival home as the mover is needed to get the van into its position on the driveway.