The "seatbelt" light on the dash is on. Does that mean the airbags don't work?

The air bag light on means the air bag light has been disabled.Yellow connectors are usually air bag circuit connectors.Is your air bag light on?

Sorry, I said seatbelt light but meant airbag lignt. Yes, it is on.

Does the yellow plug come off the bottom of the bottom seat cushion?If so thats your passenger present air bag sensor.That tells the air bag computer if you have someone sitting in the passenger front seat.Plug that connector back in and start the vechile see if the air bag light fkashes then turns off.Let me know what you find.

Problem: when they removed the seat to modify the van, the wires are cut! Yes, it comes off the bottom of the seat cushion. So I guess that means the passenger air bag won't deploy in an accident. Hm, wonder where the wires are connected? Is this somethning I can do or do I need to take it to a dealer?

I would talk to the ones that did the retrofit and have them pay to have it repaired.