Assuming its the red airbag light, then it could be either connections under the seat or could be a fuse called "services2" - second from the bottom on left hand side of the fuse box under the steering column.
Did it just happen randomly ?
Note, the warning light needs to be reset using a diagnostic - it wont go out by fixing the problem (i.e. new fuse or loose connection).
I also have a 166 (and a 156 before that) and I use this diagnostic kit to reset and check codes (www.alfadiag.net
) -- works perfectly and reads all specific alfa codes....
(fiatecuscan also works http://www.fiatecuscan.net/
If you are pulling out fuses or checking wires, make sure to disconnect the battery otherwise you willl make things worse....
(finally come over here http://www.alfaowner.com/Forum/ireland/
for best Alfa advice and not the tripe that usually goes on here...)