On the older air bag systems there is nothing to reset or code to erase. On the newer model I believe there is. Worn brushes (regulator) or a bad alternator could cause the low voltage.
djankov, one other test to try. When the light is on, try honking the horn. Sometimes when the slip rings are worn the act of horn honking causes the spring loaded contacts to connect with the slip rings. I believe any time any portion of the SRS system is out of the loop the light will trigger.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.