hey ho
So about to fit towbar to my 06 b40, there was one previous as can see witness marks on chassis and loom just cut of and taped over, geuss previous wanted to transfer to newer truck.
anyways what s the way to go about putting new socket on , anything out of the ordinary ? and should there be some sort of warning light on dash when in use , if so what wiring should I be looking for.
thanks in advance. bert

7 pin towing, would be the usual fit. The variations are - 7n+7s or 13 pin, if he was caravanning etc with it.
Towbar wiring colors and purpose <-- this should help you get the right wire in the right socket.
Personally if he's chopped the loom, i would solder in a new length of matching multicore.
One final note with regards to sockets - if the trailer has LED bulbs you may experience weird side effects.

well havent looked back along loom to see if it has relay in line, shouldnt there be some kind of light on dash as well? thanks by the way .

It's all cables, as Mits is quite decent about putting all the control units/relays and such up front usually in the bay or in front of your right knee! The lights are merged afaik, and only the indicators will indicate a trailer fault.

from what I can find out most trailers are now 13 pin, so will get a 13 pin socket and fit that if it ever stops raining, can always use adapter back to 7. thanks

13 pins are now very common but if you're towing a trailer rather than a caravan 7 pins will suffice. I seem to recall that the only reason I fitted a 13 pin to mine was to keep the fridge powered up while travelling. The sparky fitted a relay behind the rear seats in my double cab.

end of the day, as long as you have the legal 7, you can use the other's for anything relevant - adjusted on the trailer side. ie, a worklight or something like that.