Tucpal is right, it's a yellow square connector clipped to the underside of the seat. Check its connected properly failing that the pretensioner may need replacing.... Which is £'s!
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Picture from when I did mine
Sent from my LG G4 using Tapatalk
Sent from my LG G4 using Tapatalk
Picture from when I did mine
Sent from my LG G4 using Tapatalk