Hi Douglas
My advice to you is to contact Paloma at Hedleys towbars and buy a Westfallia detachable.
Then go to Volvo and buy the towing module for a Volvo fixed towbar ( they are very secretive about this and reluctant to sell it Volvo Pt No 31454602)
When you have installed the Volvo module get them to program it they will tell you there is only one download available and that is for the swing bar and the download will not work with any other make of bar Nonsense the down load you require is Volvo pt no 31435637 this will activate all the towing related functions.
DO NOT USE AN AFTERMARKET ELECTRICS KIT AS THIS ONLY ACTIVATES THE ROAD LIGHT.
The above does work all this info came from a Volvo contact of mine in Sweden
Link to towbar thread on this forum
https://www.volvoforums.org.uk/showthread.php?t=297185
Hope this helps