Aux (Thumb) issue on 303C CR

Hi all, I am having an issue with the thumb being pressurised down with no input to the thumb switch. The thumb used to work normally. The thumb will stay where it is (unpresurized) when we start the excavator until we touch the switch. If we don't touch the switch after a new restart, all other controls work as expected. We can operate the thumb with the switch but if we let go the switch, the thumb is persurized down. I guess this may be electrical as the problem starts after touching the switch for the first time after a new restart. I guess there must be a form of signal sent to an electric component actionning the AUX valves. Is there any place where we could get the electrical/hydrolic schematics to help diagnose the issue ? Any advise on the issue ? Thanks