Right, getting there. The control unit will be the AP22 (Simrad). The rudder feedback unit looks like an early rfu300 - or maybe a RFU25 - is it possible to read the label?. Whats the AP computer? J300X, J3000X maybe? The type of computer dictates the particular rudder feedback unit required.
Anyway, step on is to do a factory reset on the AP, and then run through the setup procedure (in the install manual) again to see if the issue goes away.
If the rudder feedback unit is faulty, or non linear, then the rudder test procedure in the manual should cause the setup to fail.
I think I have a working 2nd hand feedback unit, and, if not, then there is a new one still available that should be ok.
Let me know the AP computer model, and how you get on if the reset doesn't fix it.