Hya I had the same prob and I had a volvo towbar fitted and discovered that the rear earth connectors were not doing their job, so diconnect the earts at this point and clean them, it works. If you check the forum you will find a topic on this point which i posted some time ago. cheers.
--------------------- сумки, клатчи, косметички,мужская кожСтильная одежка от VERGANS!!!