I expect this has been posted before and apologies if it has. I want to fit a towbar and was wondering if a dedicated wiring kit was essential for a 2003 Berlingo 1.9. cratch:

I recently fitted a towbar to my 1.6 petrol 2006 berlingo, the only thing that is necessary is a bypass relay, around 15 quid

Dedicated wiring kits are unbelievably expensive.
http://www.towsure.com is a good place to try.
Single electrics are pretty easy to fit, although I was in a rush and got local tow-bar fitters to do it @ £35. (One hours labour.)
The grey 12s socket has less wires but requires a split charge relay and a wire running from back to front (battery live).
Most single kits come with "flasher" relay.
All good unless you are talking about the more modern 13 pin sockets. Not a clue; never fitted one. But you can get 13 pin adapters.

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Oh, and canbus systems are even more complicated. And expensive.

Thank you for the reply you have saved me a few quid.

I got a genuine Citroen wiring kit from my local dealer for around £35. It was for my Mk2 2006 Enterprise van. It fitted straight onto the connections at the rear light clusters. One to each side then run the bare wires on the ends to where the lighting socket is on the towbar. No requirement to interfere with the BSI unit or any other electronics. Only thing that I was not happy with was that there was no indication either by sound or warning light that I had a trailer connected. By law there must be some indication. Dealers did not want to know/ not interested. I bought a buzzer from the local trailer spares outlet for £4 and fitted it to the indicator wires at the rear. Problem solved. Foglight on the van disconnects when the trailer is connected as well.

Dedicated wiring kits normally have speeded up indicator clicking to show indicator bulb failure. This is apparently legal & audible warning is not needed.