@Denali N DOO, based on your description of symptoms, betting you've got a bad wire in the harness where it passes
between the body and the door. Be prepared to probe the wire, as the break can be in the wire and not show in the insulation.
Since you're testing 12V circuits, you need to have the meter at 20V based on the divisions you noted earlier. Anything lower, and you
put it out of range. Higher, and you may not be able to differentiate voltage from "noise".
@bleu7, if you're checking the filament lamps, not the LEDs, use Ohms, not voltage. Most meters have an audible continuity
setting that can usually help check for a blown bulb or fuse. If the bulb checks good, then check for corrosion on the socket
contacts. Once you see that they're clean, then check for voltage. If there's too much corrosion, you'll never get a decent
connection with the tester.
Good Luck!
Chris