Bought a BRZ stereo for the Impreza, can't find correct writing loom for it though. Any help would be great thanks

 

It came without anything? Try Halfords, at least you can see what your looking for.

 

No just cage, guy upgrading his headunit. Bought a loom but wrong one.

 

Having looked at a BRZ workshop manual it is Toyota based rather than Subaru's familiar layout.
Attached is the Audio wiring from a 2014 US model if it helps although I think the BRZ is GT86 based apart from the engine.

Looking at a Toyota ISO adaptor the sockets for the loom plugs (on the left) look similar to two of the sockets you show on the radio



which appear to be for one pair of speakers. The rest are supplied from a linked separate amplifier