Airbag Warning light came on in my 2002 Ford Explorer. I had read in different forums that the problem was resolved by removing the connector pin clip at the top of the pretensioner, sqeezing the pins together slightly, then pushing the connector back on. I did, and the airbag warning light went off. I referred to "ncranchero" post below, to see what the pretensioner looked like.

 

Thought I write this as to give back to the community, since I find lots of answers to many problems on the net. I bought a 2002 Mercury mountaineer a month ago at a very good price with an air bag light on. Thought I would just need to buy an airbag. I was getting 3 and 3 Blinks (code 33). Through reading many forums I started by disconnecting negative wire for half hour for safety reason prior to starting the test on the pretensioner connection under the seat. Cleaning the yellow connector did nothing for me, but follow the female side of the yellow connector to the pretensioner and there you will find another connector (black). Clean it well with electrical cleaner and it should fix you problem. Here is a more detail look at how I tested and resolved issue. Look carefully at the male side of the yellow connector and you will notice two plastic probes that when connected to the female side it ungrounds the connection, so you can check for resistance with a multimeter. Refer to this YouTube link it was helpful . I inserted the end of a small tie-tie straps into the grounding clip (But you can use anything that is not conductive and fits) and left them there while I tested for Ohms with a multimeter. First the driver side read 8.5Ohms. I then tested the passenger side and it read 3.6Ohms. So I figured one of the two was not correct. I then removed the driver side seat, removed the pretensioner from the seat, disconnected clip that's attached to the actual pretension cylinder, Disassembled small black clip to easily get to the wire for testing and cleaning. I cleaned the male pins on the pretensioner and the female side on the black connector. I then reassembled black clip and reattached to pretensioner. And tested the yellow female clip again and this time it red 3.7Ohms. Close enough for me compared to passenger side reading of 3.6Ohms. I put everything back together and airbag light has not come back on since. Hope this helps someone and saves them some money.