Help, no airbag light.

Upon starting the car, 2006 Aygo. All the self test lights work as normal except the airbag light, it doesn't illuminate at all. Any ideas why this could be?

Thanks in advance 

Was it working at some point if you just perchased it then go back to the garage unless it was a private sale.

It's my first car and  only had it a couple of weeks. I have recently had a new Battery fitted as part of a service and only noticed it not illuminated today. 

FIXED!!!! After spending hours fault finding, from fuses to plugs, obd scanning and stripping the centre console to get to the SRS unit..... It was none of that. I striped the speedometer and it's million plugs at the back, accessed the LED's only to find black insulation tape stuffed in the airbag light hole and taped over 🤨😳. So I have removed it, refitted the speedometer and hey presto I have an airbag light. It also doesn't stay on. I'm guessing it must have been faulty at some point 🤷‍♂️. I never even noticed the lack of light when I bought it.