radio arieal

[wobbla]

Hi,im not recieving MW stations and can only get strong FM signals.My car is a Mk3 1.4 golf AEX on a R-reg and has a roof arieal tailgate side.I have taken a fully working radio/cd from our other car to test in the golf but i still dont get MW stations.There is a thin black wire trailing from underneath the arieal mast in the roof.Whats it for and where is it supposed to go.This black wire ends up in the radio housing but then is connected to a blue wire and this in turn is just lying ther not connected to anything.Should this wire be connected somewhere to get the radio signals.Please help if anyone knows or has had the same problem and sorted it.thanks in advance.

[BobProperty]

Without knowing which aerial you have, I can only talk generalisations. A number of aerials have an amplifier to boost the signal and this needs to be connected to a wire on the radio head unit (HU). A HU may have the following wires out of it:
Permanent power for keeping the settings
Ignition power for actually powering the HU radio/CD/whatever
Earth
Illumination to match the dashboard illumination levels
Phone mute to signal to the HU to mute or divert phone call sounds
Signal to signal to external amplifiers to turn on when the HU is on
Antenna to trigger an electric aerial to open or close