OK, don't groan too loudly... but the problem has been discovered. It's a little embarrassing!
The time away helped me calmly rethink everything. On a hunch, I brought out the extension cords, the V-box, and some good quality smaller gauge wire to the actuator. Let's give it a go. Yes! Movement! It was the wiring all along. Although I used the multimeter and got a reading, I am so inexperienced, I probably didn't do it correctly. And getting so wrapped up in the technical stuff made me forget the simple things... Now which wire was it? I have looked at the sensor wires over and over again. They seem in pristine condition. I looked more carefully at the motor wires. I followed it along to the ground, where the recent warm weather and rains have made the weeds start to grow tall. I pushed the grass away and lifted the wires up, and there it was. A chipmunk must have munched into the insulation and exposed the wiring sometime over the winter, causing moisture to get in and leaving corrosion behind -- all several feet away from the actuator in the positive wire to the motor. I had just enough extra unburied wiring at the dish to splice the better parts of the wiring together until I can afford more time to properly redo it. Hooked it up to the V-box and STB inside, and works like a charm. But, I do appreciate all the suggestions. I just should have double checked the simple things. Still, I'm not sad I played with a multimeter and practiced replacing a sensor. Those skills will be useful again.
So, two less serious questions:
1. What might be a good protective barrier against critters who like to eat wiring? I am thinking along the lines of PVC pipes and insulation... but then there's the problem with water and ice getting in there. Ideas?
2. I've just been connecting wire directly into the terminals of the ASC1 and the actuator, but would feel better if I had some terminal connectors heat shrunk on the end of the wires. What would the "stud number" be on the ASC1? These are #8s for example:
50 Heat Shrink Spade Fork Terminal Connector Blue 16-14 GA AWG Gauge #8 Stud | eBay