There is a extra black wire that runs with the coax aerial cable from the aerial booster(?), behind the side air vent at the base of the windscreen, to the car radio. What should it be connected to?

Thanks

 

That is the power supply for the antenna booster. It should be connected to a lead from the radio that is powered when the radio is on. There is usually a suitable power antenna wire or amp trigger wire on most late head units.

 

Many thanks Wally, I will try connecting it properly when I get back to the UK. Ever since I've had the car the black wire has been connected to the radio chassis, so it will be interesting to see if the receiption improves (although it always seemed ok to me).