volvo towbar

[Fons]

Im am sorry for my englisch, i am dutcht.

I own a Volvo S40 1.8 Sport Edition from 2001 the milige is 210.000 KM color 335 green The car is made for the dutch (EU) marked and is Left Hand Drive.

to pul a caravan a towbar is mounted to the Volvo. the electrical connection is by a 7 pole connector.
Behind the lefthandside rearlicht there is a gray connector specialy for the towbar. On the connector is a black wire and a yellow wire. the black wire is for ground the yellow wire is connected to the towbar on contact 2 (continu 12 Volt or rear Foglamp)

The problem is that the yellow wire is never giving 12 Volt!
not when the contact is swiched off
not when the contact is swiched on
not when the lichts are swiched on
not when the lichts are swiched on and the engine is running
not when the rear foglamp is swiched on

how can i get 12Volt on the wire? i dont like to change the wiring of the car. The dealer does not know Volvo tels me to let the dealer find out. I dont like to invest in dealer knolidge, they should know!
I have looked at the wiring on this webside, but can not find out whare the yellow wire is going.

i hope there is sumbady who can help me find out what the matter is and helps me to solve the problem.

[coustyj]

How about brake lights?