Focus MK1 Warning Light

Hi, sorry if I have posted this in the wrong place. I am hoping someone can give me some idea, any idea!

The airbag warning light has been coming on on the car for some time now. Garage (family friend so trusted) has checked the clock spring, the wiring etc. under the drivers seat etc. but nothing has worked. It's flashing code 22 which is something to do with the drivers side airbag. Anyway, took it in again the other day because the garage electrician had been brought in to check it. He spent several hours trying to figure it out but to no avail. The diagnostic machine said at first, it was the driver's seat, then, after he fiddled around with the wiring it said passenger's side seat. The general theory now is that there is a wiring fault somewhere, they think under the front carpets. I have heard though that sometimes there are issues with the fuse box? Does anyone have any ideas on that? After I picked it up from the garage the light stayed off for a day or so but then, driving a couple of days later...it came back on. I think, think, it may have occurred when I went up hill as odd as that sounds. I am not aware of any leak at the front of the vehicle but there is a leak on the tail light on the passengers side. Any help or opinions or advice would be really really appreciated. Thanks. Gav