Hi Nigel
As I remember, the connector for the amp is on the front, and you can easily splice into the mute wire there (I think you may have to take the glovebox out though - it's a while ago and I honestly can't remember). The diagramn I sent you has pin numbers on it which correspond to the picture of the plugs on the other diagram (I hope that makes sense)
I certainly remember it being quite easy to do though mate