Norm,
I had a similar issue with my 01 Contessa. Checking and cleaning the grounds didn't solve it. The problem was wire size. On mine they used a plug /pigtail to connect the wall switch to the wires going to the slide motor and brake. The pigtail was 14awg but the wires to the motor were 12awg (if I remember correctly). Removing the pigtail and connecting the motor/brake wires directly to the switch solved the problem.
Steve