[Rversteeg]

The airbags in the seat of a 940 are mechanically actuated, so they are not connected to the SRS light at all.
A few years ago I took the attched photo in the Volvo museum in Göteborg. In the front you can see the yellow actuator device. On a side impact a pin in this actuator is pushed in by a filling block located inside the door. This will activate the seat airbag, nothing electric involved.
By the way, when you take out the seat, don't let is drop on the actuator side, as this might activate the airbag as well. You probably found a red cap hidden somewhere behind the plastic side cover. This cap can be used to cover and secure the actuator when the seat is out of the car.
Did you by any chance have the steering wheel removed? It takes a special precaution not to damage the airbag contact reel when removing the steering wheel. If you do not follow this, the contact reel will be damaged and the SRS will light up.
I am not sure about a RHD car, but on a LHD the airbag control module is located on the floor, underneath the driver seat. It has its own, rather thick orange coloured cabling system, separate from the other wire looms.
Rob