If the towbar has been fitted before there should be a cut out under the bumper. The slots for it are already there and it's an easy fit after the bumper and crash bar are removed.
The instructions are on the volvo website. Just find your car here.
http://accessories.volvocars.com/en-...2013/D5/Manual
The wiring module plugs in and is programmed by the dealer to activate the anti-sway feature.