trailer socket converter, and fuel economy

[pauper]

We've recently bought a 2013 Fabia 1.6tdi 105bhp, and i thought the forum might be interested in our fuel consumption findings.  The Fabia replaces a diesel Fiat Panda. It is quite a bit bigger and heavier, and considerably more lively in terms of acceleration.  We were therefore expecting some penalty in fuel consumption.  However, our first tankful, measuring brim to brim and ignoring the trip computer, averaged 66mpg, which is about the same as we used to get from the Panda.  Our second tankful, which included a long trip from west wales where we live to Hertfordshire, averaged 70mpg, which is rather better than the Panda under the same circumstances.  Unlike the Panda whose trip computer was a few mpg pessimistic, the Fabia's is a few mpg optimistic.

 

The second point is about towing and the trailer socket. Our Fabia has the factory towing kit, with a removable towbar. Today I tried towing for the first time.  Before I plugged in the socket converter (13pin car socket to a socket accepting 7 pin trailer plug) the rear proximity sensor went bananas when putting the car in reverse, but when the converter and lead are plugged in you get a lovely picture of a trailer on the display! 

 

My question is, when plugging in the converter (which bayonets into place nicely, and can only fit in one position) the car's sidelights come on, and so do the trailer's when its lead is connected. Is this normal? A sort of involuntary volvoisation when towing?  Or is it a fault in the socket converter?  All the other lights on the trailer work ok.