In case others are interested... we asked a Raymarine electronics technician to diagnose our "dead" autopilot... was the display dead? Or the computer? Or the cable? We could not tell. It took him 30 seconds -- he looked at the FUSE for this device. It should have been a 30 amp slow-blow kind. Instead, it was a 5 amp slow-blow and it was blown. He installed a 30 amp fuse. Autopilot works fine now.
2006 34' PDQ PowerCat "All Heart", Bellingham WA