Problem with ST4000+

[dohagen]

The belt on my ST4000+ broke. After replacing it, i could not get the wheel to turn properly while it was disengaged. So I bought a replacement wheel which turns out to be the EV100 wheel. I installed it and used the old cable as it would be a nightmare to replace the old one. When I tried it, it would not hold a course. It would begin with small adjustments and then begin over correcting first one way then the other until I looked like a drunk weaving down the river. I tried adjusting the gain to no avail. I also re-swung the compass and adjusted the heading to match the boat compass. Now that holds until I engage the autopilot and it changes. Any suggestions as to how to get this to work properly?