[Kevin Sevcik]

If you're using the solenoid breakout and have 12V wired to it, I'm liking your theory of the excess ribbon cable touching a 12V circuit on the solenoid breakout. There's plenty of chips on the sidecar that aren't expecting 12V and aren't likely to survive it showing up on an unexpected pin. Even moreso if you're powering the solenoid board with 24V.

The solenoid breakout and module is likely fine, since it's rated up for the voltage it's carrying. If I'm reading the spec sheet for the 9403 module correctly, it can withstand +-30V on the inputs with no ill effects, so it's probably fine as well. Wouldn't hurt to test all the channels you'll be using, however.