Have you checked that out? It will be a box with some linkage connected the quadrant or a variable slide resister about 18 inches long connected in some fashion. If the motor is working correctly and the steering system isn't locked up and you don't have a significant voltage drop and you have a new control head then their isn't much left. Pretty much all you have left is the fluxgate compass and the rudder feedback device. I have no knowledge of your system but the components do pretty much the same things in most units I've seen. If what ever tells your system where the rudder position is, is not sending the information to the control head then you will get some sort of rudder error message. If you had a hydraulic ram system I would say that it was probably the fluid in the ram bleeding by the piston and not moving the rudder far enough. That would send a rudder error message because the rudder feedback info wouldn't match the control head. Sense it's an electric drive without a clutch issue, then I would say that it might be what ever sends the rudder position info. B and G pilots usually have a variable resistor on top of the ram that moves with it. My system is an electric motor and chain drive connected to a ComNav head which has a stand alone feedback box connected by linkage. Maybe you don't have anything external but it seems to me something must send the rudder position to the head. Just some thoughts. Good luck. This kind of stuff is a B%$ch.