Thanks, Trialex. Was in a similar situation with optoisolators. Couldn’t for the life of me figure out why my voltmeter was showing 0.0 for pin 13, but when I’d try 7 or 9 or any other pin, I was getting 2.2V at rest. Pulling my hair out trying to figure out if my bad EE skills had fried my Arduino/isolators-- Nope. Skipped a line. Silly. Thanks again.