Not sure whether you have a saloon or tourer so I'm not sure what you have missing. It sounds like a tourer, and if so only one of the two patterns should be connected, the other is for TV.
The most likely problem is the new radio is not providing power to the antenna amplifier module which is located just above the antenna if indeed it's a tourer. There's a single connector for the power and you can test to see if it's getting 12v on it with the radio on. If not that's your poor reception cause.