Looking at Costco they sell Greenball tires for TT’s they say their made in California.
I don't think we have any radial ST tires made in the USA. Better double check your source.I think they are made at the Port of Long Beach. A big floating machine spits them right out.
Autorange is easy to check by using same sequence testing on the battery direct.
Still does not explain stuff burning up.
My first thought was malfunctioning converter and no battery or battery disconnected.
20 volts does seem rather odd. It should be tied directly to the battery through the 12v distribution system. Seems like some other power source is bleeding into this 12v outlet. Is the 12v connector OEM or added after the fact? Where is it connected?
I would find the fuse that cuts power and check voltage there. Possibly a poor ground back feeding through some other system.
Avoid busy would be 6a on Sunday morning. Otherwise rush hour starts 8a Sunday and goes through Saturday night.
210 to 57 can also be very crowded (not as much) and a few more miles.
Roads are fine for 55 mph travel if you ever see that speed.
Traffic reports on AM 980 or 1070.
The 12v feed does come from the grey box up in the ceiling however there is no fuse up there afaik. Good to go up there and check 12v power though.
I think the fuse will still be part of the stack near the converter. Just a likely to be a bad connection up near the grey box.