Regarding MIA's problem with the autopilot going the wrong way, the two wires to change over are the power leads from the course computer. Where one wire currently goes to the positive connection, change that to negative and negative to positive, and that's it job done. As for the initial set up procedure, if you don't have the original hand books describing the commissioning procedure, go online to Raymarine, and download the instruction from their website. Commissioning will involve taking the boat out, setting the instrument to "Learn" in accordance with the Raymarine instruction, doing at least two full circles slowly, then setting the boat to steer a suitable course under autopilot. At this point the boat will initially wander a bit from side to side as it learns your boat's handling characteristics, eventually settling onto the course you set. Thereafter the job should be a good one, so good luck. It's very satisfying when the end result is what you wanted.
As for repairs to chart plotters, take care who you instruct to deal with the problem. I had an old RL70 plotter that could also handle a radar input, but which had been badly neglected by charterers during the boats early life. The first repairers I sent it to had advertised on a popular web auction site, but they did nothing and charged me for doing it, saying that the internals were corroded etc, not worth repair etc., but they had not even bothered to take the plotter apart. I then sent it to Raymarine and they did a proper job of repairing it and their charges were fair and reasonable and the plotter continued to work. Eventually I changed the plotter for a newer version that could also display in colour, and gave the old one to a friend who has continued to use it.