Well... i let my self get the better of me and i couldn't let it go :doh: that little switch inside the socket that stops the cars foglight going on when the trailers connected. fired up the Elsawin and started trailing through wiring diagrams until i found what i wanted and it explains why there's so many wires
as it turns out the switch is separate to the socket wiring, differs from normal aftermarket sockets that switches the fog output. this has a fog live all the time to the trailer socket fog pin, and another down to the switch, then back to the foglight bulb. it has another wire when switched that goes to the parking sensor control module. when the trailer socket is inserted it pushes the switch which earths a little feed from the parking sensor module, it must be a small voltage as it doesn't illuminate the bulb.
when you go into the wiring diagram for the parking module wiring diagrams it shows this socket switch connection to the switch going to pin 5 on the module, a red/white wire. So, located the parking aid module,
unclipped the plug and sure enough there it was
fired up the vagcom and one of the blocks shows trailer: no
i looked in coding of the parking assist module and the first digit is Trailer Hitch, changed the 0 for an 1
connected an earth to this new wire i've found
and every time that is earthed the the trailer status changes to yes
cracked it
so now i know it is going to work i could wire in the socket properly, started by interrupting the fog light feed
and running it down to the socket wiring
and running the little wire up to the parking aid
and tidying away
and i can confirm when there is a socket inserted for a trailer the
rear fog light goes out AND the rear parking sensors are disabled, as soon as the trailer socket is removed they are all reactivated.
and the internet said it can't be done
Now i was always told there was a trailer module in the system and it deactivates everything. but from the wiring diagrams i found on Elsawin it shows the trailer wiring just T's straight into the rear of the lights direct
when the car gets the signal that there is a trailer connected, via the socket switch, via the parking aid control unit, it must either modify or turn off the bulb-out monitoring module so that is can see the double load on the rear lights, thus not flagging up a bulb out fault on the dash. If this is the case then i needn't have fitted the bypass relay. it also explains why all the colours in the trailer wiring loom i received were the same as the rear lights.
Also coming out of the hazard switch is an outlet for the trailer operation warning lamp
so again when the car knows the there is a trailer attached, via the socket switch, via the parking module, it must illuminate this symbol on the dash too.