Does anyone know where i can get the wiring harness that plugs into the existing wiring on a classic impreza allowing me to plug directly into an Alpine headunit thus avoiding cutting any wires.Ive looked everywhere and no one seems to do them.Any suggestions

 

Halfords do the ISO wiring harness adaptors. They might tell you that they don't fit WRXs and STis but I've been reliably informed by my local 'proper' ICE shop that this is rubbish and you should get it anyway.