Yesterday I disconnected from shore power, the battery settled down to 12.8 volts and tried to extend the awning. It moved after rocking the switch. Once partially extended, I bypassed the wiring and connected directly to the battery and the motor moved as expected. I think that eliminated the motor as the problem.
I cleaned the rocker switch. Next I'll trace the wiring through the awning arms to see if something is frayed and then redo the connections to the switch. Glad I'm retired and have the time to play with this stuff.