I have a 2004, 156 2.4 JTD Sportwagon. I also have an airbag light that comes on. Was on when I bought the car. A few weeks later someone drove into the back of me in Tesco car park, but after the bumper was replaced the light was miraculously absent from my dash!
A few months later, bing, airbag light on again. Last night finally got around to looking behind these little plastic covers in the boot (on the side near the rear brake light cover) that are only held in by a single screw. Low and behold, as mentioned above, there was the yellow airbag cable. I gave it a little wiggle to see whereabouts the connector was, but thought I'd leave it until the weekend before disconnecting and re-connecting so that I could disconnect the battery and remove power. However, this morning the light was out again. Hooray.
So I reckon it's worth the 2 minutes to remove the covers on each side of the boot and just give the cables a wiggle. If you're not disconnecting and re-connecting you won't set anything off.