13 Pin Trailer Electrics tale of woe and fix.
 

I began the below linked thread after being surprised and not a little annoyed after my daughter's 2011 XC70 failed it's MOT due to the 13 pin trailer electrics not working. The fact that it is officially recorded as a "Dangerous Fault" which prevents the car being legally used until repairs are completed is particularly annoying and very inconvenient.
The problem is now resolved but I thought that the thread may be of interest to others who have non Volvo 13 pin towing electrics fitted to their XC70.
You will see that I also have a rant regarding the absence of a pin dedicated to charging the caravan battery.

https://www.volvoforums.org.uk/showthread.php?t=314345