But even though it was working fine, I still added an LED/resistor to one of the pins on the Arduino and updated the code in the sketch to turn on and off that LED whenever it received a garage door open or close command.
but please remember, I'm a noob, so the more detail, the better.
That works both ways. "one of the pins" is not a lot of detail, I think you'll agree.
If if works on the bench, and not in the garage, then I would suspect a wiring issue.