G01 - Aftermarket Towbar electrics issue - fog lights

[Graham2019]

Hi, I had a Towbar fitted to my X3 with dedicated electrics. All works well when towing, the only issue is the car is not turning off the car fogs when trailer connected (so you get mega glow off of front of trailer in rear view mirrors). Tow bar fitters are being pretty unhelpful, they have contacted Witter (supplier of Towbar and elec kit and booked and paid for through Witter site). Witter are not sure but they think the car needs a CANBUS edit for this to take effect when car detects elecs are plugged in. It sounds like the Towbar fitter are saying this is not up to them. Is it something a dealer would have to do and how much would you expect to pay for this? Bit peeved as I would expect this to be part of doing the complete job. Advice appreciated, thanks - Graham