Hi I've got a 2007 fabia vrs with standard head unit and I want to fit a sub with built in amp in, anyone know what adaptor/connector I need for the back of the head unit so I can plug the leads from the amp into, cheers

Not sure there is? I'd say the easiest thing is to take a feed from the rear speakers

A friend of mind did this on his mk5 golf. . .Its an rca adaptor you need. . But I dont know what you splice into. . Just the general signal wires im presuming . .

Obviously not as good as using a proper sub output on an aftermarket headunit. . Coz that would only channel the bass frequencies. . Where as getting signal from speaker wires youll be getting alsorts of frequencies going to the sub, but the amp will probably only use certain frequencies if its a dedicated bass amp.

http://reviews.halfords.com/4028/704734/reviews.htm

Something like that I believe.