Hi I have been reading very carefully, I have a 1998 156 v6 and I have just been out to look at mine.
1/ check under passengers seat to see if there is a wire - yes - but not connected
2/ turn ignition on to see if air bag light comes on before starting - no light
I have never noticed this before so will have to look at.
Just been looking at auto-data information.
upto 2000 on 156 passenger airbag with pressure sensor fitted as optional
2001-> front passengers airbag fitted as standard
2001-> front passengers airbag seat pressure sensor fitted as standard
System Warning Lamp
= switch ignition on
= SRS lamp illuminates
= Lamp should go out after approx 4 seconds
= If not requires diagnostic to check
Deactivation Warning Lamp
= Switch ignition on
= deactivation lamp on for 4 seconds
= if passengers airbag activated; lamps flashes for approx 4 seconds before going out
= if passengers airbag deactivated: lamp remains on
Note= if system has been activated more than 3 times according info SRS ecu will require replace-ing
A easy way to check for resistance is to use a 12v5w capless bulb connect to wiring plug loom side then turn ignition on to check lamp operation (this bulb has the same resistance as the components)