So when I said see if the SE wire reads to ground, I meant check the resistance to ground. If all is well I would expect to see a reading in the high K ohms to M ohms. Anything lower than a couple hundred ohms (all the way down to 0) could be the cause of your problem when the contact in the edge detector closes and puts P24 on that SE wire. If you do get a low resistance reading, you would then want to find out where the path to ground is coming from. To do that I would first pull the wire from the edge detector board and see if you still read the same resistance or it’s now open and coming from the detector board. If it’s still on the wire, the only other place that goes should be the terminal strip in the door operator. I have seen a similar issue from a metal shaving sitting across 2 shorting bars on that terminal strip.