PA60 Aerostar pilot reported a faulty directional gyro (DG) during descent. ATC offered assistance and pilot continued and landed at the destination.

Narrative

The flight was from ZZZ1 to ZZZ. En-route alt was FL190. After last enroute descent entering terminal area I was given a heading to turn to prior to the ILS for ZZZ. The Approach Controller advised that the heading was incorrect. I had experienced a similar issue on a previous leg but thought the problem had been solved (a sticking HDG (Heading)/GPS selector toggle switch). After several commanded vetors; I realized that the aircraft. was not following selected headings and the controller did his best to assist; finally giving me commands such as 'start right turn; and stop turn' This ultimately allowed a turn toward the airport. The final instruction was 'ZZZ airport is now directly ahead of you' Through a break in the cloud base I saw the airport environment and cancelled IFR; descending to pattern altitude. The stress level was extreme; as I had no idea why the aircraft would not respond in the expected way to manual settings on the gyrocompass. Once on the ground i called my avionics tech at base at ZZZZ and he suggested I check the remote compass slewing switch. This switch connects the wing tip compass with the instrument paned DG (Directional Gyro). I found it toggled in the out or 'off' position. Somehow this switch had inadvertently been pressed and toggled out. I tested its function on the ground and the compass behaved as it should. It is a switch I never check and never use. I have no idea how it's position became changed. My stress level during the many turns as the controller tried to orient me was the highest in my flying career. I give the controller a great deal of credit for his decision to employ 'turn..stop turn' instructions. He could have saved our lives! I consider this report as important for controllers as for pilots.