Airbag Warning Light On.

I have just noticed this warning light turn red when I put a bag on the passenger seat. Later I sat in the passenger seat and it lights up red. 

Any ideas. 

TIA 

ND4 RF 2018

Hi, Which model OF MX-5 do you own?

Are you talking about the car in motion and a heavy  shopping bag on the seat? If so it will if the seat belt is not on, it will think there is a passage without a seat belt.If so there should be an annoying ding ding ever 10 seconds.

Anything else its probably the stupid plug under the seat.You have probably already had a play with that.I had issues with mine after Seatsurgeons recovered my seats.

Stupid question but when you sat in the seat,you did put the seat belt on i take it?

“The seat belt warning light turns on if the driver or passenger’s seat is occupied and the seat belt is not fastened with the ignition switched on.”

Owner’s Handbook