2018 Silverado - various electrical issues

[hexamadecimal]

Hello! I’m new to this site and searched for a few terms before committing to posting. If the answer is here already I can’t find it! Anyway, I was leaving work last Friday and got a “left rear turn indicator failure” message on my dash info screen. Sure enough, the running lights work fine, but brake or flashing does not on the rear right fixture. Bulbs work in all functions when I swap to the left. Later that night I noticed my map lights do not come on anymore (I’ve toggled the switches and rocker on the overhead console), the switch backlighting on the tow brake/4wd/light panel to the left of the steering wheel is out, my under-armrest and rear 12v sockets are dead, and the vanity lights in my visors are out too. I’ve pulled every fuse under the hood and on either side of the dash to check for a blown fuse - all solid. Dealer can’t see me until 7/30. 
 

Any ideas? It’s driving me crazy that I can’t figure this out! Thanks!

[rlcole321]

Sounds like a ground issue, seems to be fairly common, start with G218 ground