I concur with what has been said.
Maybe the AUX is the Aux heater fan switch... which on later models is under the drivers side couch and uses engine coolant to heat the living area.
Mine looked like this in situ.
Like this out and refurbished.
Your horn issue.
FYI, on the chevy chassis, that horn fuse also supplies power to the 12v
cigar lighter recepticles.
If the fuse did not blow when you replaced it, then whatever caused it to blow, is either fixed or maybe intermittent...
At the risk of sounding like a salesman... I suggest you spend a little cash, and buy a Powerprobe 3... and if you can swing it, a Powerprobe ECT2000..
Best electrical diagnostic tools i have ever seen and used, and essential as a wrench for your issues!
With the PP3, you can just walk around the MH(30' cable), and at the push of your thump supply power or ground to a componant or switch, or read if something has power or ground, or is shorted.
The ECT2000 allows you to trace wires, both open circuits and shorts.
As a testimonial, a combination of these two tools allowed me to find the dead short on my Horn circuit which turned out to be this wire on the drivers side 12v
recepticle that was punctured with a trim screw!