Wacky ignition switch behavior

[IndyAnne]

I love this forum for all the knowledge here. Thanks in advance!
Problem: it has been raining, don't know if it has anything to do with anything, but...
I picked up a couple of neighbors' trash to take to the dump. Nothing out of the ordinary happened until I got there and turned off the ignition to get out and unload. Truck would not turn off.

Stopped by auto parts store because my go-to guy was closed (Pat Lorber at Apex in Greenwood). Only learned to pull the 30 amp fuse for the ignition EMC ? to stop the engine. When I got home, turned the switch off, but noticed a whining sound from near the gas tank. Scary, so I disconnected the neg. battery line. I put one of those quick disconnect devices because I've been preparing to put in a new stereo and try to troubleshoot the lack of courtesy lights including the dome light.

When I d/c'ed the neg battery, the fuel tank sound stopped. Then I reconnected the neg battery cable. It was still daytime here around 7 pm

later, I went out to get something out of the truck and the dome light was on!

And, coincidentally, the temperature gauge indicates the engine is running hot.

I've been browsing the forum and other sites, not getting much specific info.

Would replacing the switch be the fix? I know the current switch is an after-market replacement because I can't get extra keys made without paying a lot to a locksmith for a "chinese made" (pardon if I'm insulting anyone) key duplicate.

Are the engine temp gauge reading and the overhead light suddenly working possibly coincidental?
Anyway -- why would the overhead light suddenly work when the ignition key will not kill the engine?