 Seat Belt Buzzer
I also have had a problem with my seatbelt buzzer on my '02 E150 Traveler van. Couldn't find that rotten sounder to disconnect it. I want to start my engine, THEN put my seatbelt on. Meanwhile that chime seemed to chime even after I fastened the seatbelt. After snapping the buckle in and out it would eventually stop chiming. After putting up with this hassle for over two years, eventually I could not stop the chime. Had to put up with the noise the entire time I was driving. Looking under the seat I found a three conductor plug which I unplugged which stopped the chime. Now the Airbag light stayed lit. Perhaps the seatbelt switch tells the airbag how hard to deploy adjusting for non-seatbelt use? I now took it to the dealer to be fixed. When they pugged the harness in, everything worked like it was supposed to!
What I ended up doing was using a meter to determine which of the two wires on the harness I unplugged had to be tied together to fool the buzzer system into thinking the belt was fastened. It appears there is a SPDT switch on the seatbelt system which disables the airbag when the plug is disconnected.
Keep in mind when you disconnect the seatbelt switch like this, the airbag system will think you are wearing the belt causing the bag to deploy at full force which could be dangerous if you are thrown forward at the bag while it is coming at you.
The owner's manual has a complicated proceedure to disable the chime. That did not work for me, probably because the seatbelt switch was intermittant. If I remember correctly it was something like put shifter in neutral, turn on parking lights, turn on ignition, click seatbelt buckle three times, etc, etc. This did not work for me. | 
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