Well, the resolder trick worked for a little less than a month. The red airbag dash light came on consistently as I ran errands today, along with neither "on" or "off" orange passenger light with no passenger riding.
So I took the map assembly back out, reflowed and resoldered absolutely every bit of solder on both sides of the board with a much finer soldering iron tip this time. No red airbag light, and the on/off orange passenger light is working properly. We'll see...