mate you are hunting for a needle in a haystack if you don't have the fautl codes honestly.
anything yellow is airbag related.
I don't want to waste your time but as a handy hint the curtain A pillar bags often throw a fault. the connectors for these are in the drivers side rear wing, so you have to take the carpets out of the boot and fish down the side of the wing for the 2 yellow wires. often cleaning the connectors corrects this.
it is possible though that you will need software to reset the light though.
if you have a laptop, or a PC with a long enough USB cable to reach your car you can get the USB KKL cables for around £10 off ebay and there is some free software out there that maybe read the ECUs for you. you would have to open the cable up and change one wire to a different pin for airbag ecu though.
have a look at the FiatECUScan website to see if you car is compatible. if your planning on living with an alfa for any length of time I would recommend getting a cable!
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso