I've replaced the drain motor and air gap. Checked the drain hose for blocks/kinks, tested overflow, raised drain hose loop on the way to the air gap as high as it goes. Hose from air gap to disposal is clear, plug in disposal inlet removed. If I shop-vac water out of the sump, making a seal by wrapping a rag around the hose, it will run one cycle.
I *discovered* the HUMIDITY SENSOR above the drain in the sump. Can anyone tell me if this is part of the drain or startup cycle? The thing costs $15, so I'll replace it on principal if it's involved. Otherwise, I'm running out of the cheap stuff and face trying a new control module -- not so cheap.
One last thing, which I'll try now, does there need to be another drop in the drain hose between the high point and the air gap?