I just went thru this mess with my XJ. Not quite the same, but very similar: thrown code for undervolt on TPS. The kinda crazy thing is that all the systems your describe (except the horn) share the same ground. And the horn shares the clock-spring connection. Its all interrelated... which makes troubleshooting a major PITA.
What I did to diagnose my final fix was pull the horn relay. Yes my horn was working just fine... but I had come across that post for a slightly different problem. All of the sudden my TPS voltages were normal. I replaced the clock-spring and then reinserted the horn relay and all was well. What was happening is that there was a short between the common ground for the cruise/TPS/IAC/"lots of other sensors" and the horn. My horn worked fine as did my cruise, but my idle was all messed up and the CEL was on.
The lesson that I learned on that one is that shared grounds suck for troubleshooting. Something that you think may have nothing to do with it... does.
that being said:
I would try to disconnect the cruise control portion of the system and see if that has an impact on the airbag... you can also try the reverse, but only if you are comfortable working with the airbag system. Biggest thing to remember is that you need to dissipate any remaining charge in the system. I have seen posts online that it will take anywhere from 2 minutes to 30 minutes. I disconnect both battery terminals and clamp them together for 10 minutes, and thus far I haven't had an issue.
A side note on that - the batter terminal procedure that I just described will also more than likely reset your computer. This may clear the SRS light, but it will also mean that the computer will reset to defaults for performance. It will take several full driving cycles to relearn. Not a big deal, but here in Colorado, it does some adjustments for high altitude, and I see you are in Leadville... so those adjustments will be more pronounced. not a big deal, just something to keep in mind that you will probably get worse gas mileage for the first tank after the computer reset.
Having gone thru this hell with my XJ, keep this updated and I'll share everything I can with what happened with me and hopefully that will help. Welcome to the group!