I guess you mean the rear connectors for the sensors ? You can find them above each shock mounting point. Remove the fabric covers on the left and right rear sides in the boot, and you'll find them. Others have taken photos of where they are, so have a search on this site, and it will be easier once you've seen the photos. They are only held in by velcro.
On my 1.6, the connectors that failed first, were the ones under the front seats. Both of them are horrible orange coloured connectors. Then the one in the compartment reachable from inside the glovebox went next. That one was coloured yellow. Search for that too.
Before I hard wired and removed the orange connectors, I had airbag failure light up on the dash when the car went over a hard bump or two. It didn't happen everytime, but pot holes were the worst for triggering a "beep beep beep"
Well if you do decide to go the hard wire method of removing the connectors, make sure you know what you are doing. I wouldn't recommend it if you don't have at least some basic electrical skills, and understand how to solder. You must be careful not to short the wires out somewhere too. Even to the chassis.
To fix my airbag failure problems, I ended up hard wiring and removing the 2 orange connectors under the front seat, the 2 in the rear (above the shocks), and the yellow one above the glove box (passenger side). This sorted the problem. I did this in the period of about a year. Though a few weeks ago the OCS sensor failed ! But rather than buy a new OCS, on this site I read about these people selling an OCS simulator
http://stores.ebay.co.uk/Airbag-Steuer-Systeme
So I bought one. It actually does the job. The only drawback I see is that the passenger airbag will always go off in an accident. But I don't see that as a big drawback. You can turn the deployment of the passenger airbag off anyway, with the key. I guess handy if you have a child seat. I think fitting a new OCS mat is a bit more work that fitting this black box. Also search the site to find the symptoms if you have this. Others have written about this problem in greater detail.
But from your problems you describe, it sounds like you have bad contacts in the horrible airbag circuit connectors. I would open, clean, then click back together the connectors under the front seats first, then the yellow one above the glovebox. That doesn't take much effort, and will hopefully sort the problem for 6 months or so until the contacts get bad again. You can use contact cleaner to cleans the metal connectors, just be careful where you spray it, and read the instructions on the can. Using WD40 is an option too. It will buy you time to decide if you want to go the hard wire route, or I also believe Fiat offer a connector fix, but you'll have to pay for that I expect. Not sure what the fix is from Fiat, but I expect it involves swapping out the old connectors, and fitting connectors that actually connect !
Shame on Fiat to fit such poor connectors for the airbag circuit. They just don't do the job. I guess they didn't test them enough, as after a few years they fail. I wonder if anyone has actually crashed their car, and the airbags didn't go off because of faulty connectors ? Should Fiat really be cutting corners on parts that are related to safety.
Good luck sorting your airbag problem out
