www .seatcupra.net/forums/showthread.php?t=87344&highlight=alana+mini+iso&page=2
Have a look at the 2nd photo, the connector replaces the unused yellow plug. The RCAs connect to the amp along with the blue cable for remote power on. All you need then is power and speakers connecting to the amp.
I can't post links so remove the space after www
On the amp/sub will be terminals +ve, -ve (or GND) and REM. The Blue wire from the yellow PC3-11 autoleads plug goes to REM. That will then switch the sub on when the head unit is turned on.
Hopefully that makes more sense
I used the earthing point in the boot which is just inside on the left behind the light.
Getting a feed from the battery was difficult for me, the cupra tdi has no room in the engine bay to get access to any gromets. In the end I went up the passenger side wing, down the door crack and in through a gromet there. The cable can only be seen if you are looking for it with the door open so was fine for me. I'm sure there are other places but I found it to be the easiest and most knuckle friendly