Trailer control function disablement

A trailer vehicle function control system comprising an electronic control unit, which electronic control unit is provided with a standards compliant communications interface adapted to communicate wirelessly with a remote electronic device. The communications interface is adapted to actuate control of functions on the trailer. In use, the electronic control unit is adapted to measure the signal strength of signals received from the electronic device, wherein if the signal strength is below a pre-determined level, the electronic control unit disables the actuation of control functions by the electronic device.