After an ATC vector; the Controller notified a BE20 pilot of his aircraft's heading error which was found to be about 80 degrees. The heading source was switched to number 2 and the flight continued until maintenance was addressed later.

Narrative

[I was] climbing out in the morning through mixed VMC and IMC. [I was] assigned right turn to 260 degrees. I set heading bug and watched airplane turning the correct direction. I then proceeded to go through the climb checklist. I watched the airplane stop on the assigned heading and continued the climb checklist. I glanced at [the Garmin] 696 and saw that the airplane was on an approximate 180 degree heading. I compared it to the pilot HSI and considered that perhaps the [Garmin] 696 was not updating for some reason. ATC advised that they instructed me to make a right turn and I had actually made a left turn. I then compared pilot HSI to co-pilot HSI and wet compass. I realized that the HSI was off by approximately 80 degrees. I advised ATC that I had an autopilot issue. They switched me to Center and I advised that I needed a heading check. The HSI slowly came back to a correct heading. No other problems in flight once I determined what the problem was. Landed and contacted contract avionics. We went through trouble shooting and noticed that pilot HSI would not slave. Co-pilot's would. At the end of the flight; the HSI was basically on the correct heading. The Avionics Technician advised that I should taxi around to see if it had aligned again. It seemed to be correct. They advised watch for more trouble and we would switch gyros when back in town. I operated off of #2 drive for the rest of the flight and put [it] in maintenance the next day. Avionics advised that they switched gyros and just watch to see if problem goes to co-pilot's instruments.