Well, the warning light came on two weeks ago on my 2006 2 door Rabbit, and it was due to the driver's side seat. So I checked underneath, and it looked like the splicing with butt connectors was done by the dealer. It must been a long time ago'cause I haven't been there since 2010 or so.
There is no fault on the passenger side, and when I checked, the connector is still there on that side.
Anyway, they added about 2 inches of patch wire, and there were 6 of those crimps with adhesive tubings. Due to the glue, wires weren't moving I pulled, so I figured I'll just try crimping them again. And I blew some air to the connectors on the floor to clean up any debris that might've gotten in there.
No luck. Warning light came right back up after clearing.
There was a post saying it might the actuator that's failing, or it could be the seatbelt wiring. Well, the easiest for me to try first was get rid of those crimps. So I snipped them off, and solder them good and heat shrink them with adhesive tubing, and tie them around old connector so they don't move around much. Maybe frequently moving seats back and forth might have loosened those patch crimps.
Well, it worked! I cleared the fault and it's staying off! I don't remember what was it like before('cause I never paid much attention before), but the airbag light goes away with a slight delay of second or so when I start the car. Maybe that's normal.
And as mentioned by OP, I turned it on, connect the battery, wait for throttle body, and do the windows reset(open and close few times) and it was all good to go. Warning light is staying off since last week. I jiggled wires few times and moved seats several times and so far so good!
So if anybody has their light came back on, follow the OP's wonderful instruction and try soldering them.