Curtain airbags are the ones which deploy from the edges of the headlining in the event of a serious side impact. The connectors are located each side of the boot (SW), behind the carpet, not too far from the back of the rearlights. Look carefully and you should see a small plastic cover, kind of triangular in shape, held on to the carpet with a philips screw. Remove this screw and gently pull the cover out: the yellow airbag connector should be clipped to the rear of this cover, but they often fall off, so you'll have to look in the hole in the carpet to find it. Easier to find on a saloon, as they are both on the drivers' side, and the whole carpet can easily be pulled away, as it is much less rigid.