General aviation instructor reported smoke in the cockpit during cruise on a training flight. The flight diverted to an alternate airport and landed.

Narrative

While conducting instrument cross-country flight training enroute to the ZZZ airport we experienced an autopilot pitch trim failure CAS message; which procreated into an electrical smoke in the cockpit unexpected zero time threat. Upon the identification of the electrical/rubber burning smell I discussed and briefed the situation with him. we made the decision to divert to the ZZZ1 airport. Firstly; we continued to maintain positive control of the aircraft and shut down the electrical system using the battery master; since we were in VMC conditions. After securing the battery master the smoke started to dissipate. At this point I tried to regain communications with ATC and ventilate the cabin. I started by pulling all of the circuit breakers in the avionics bus tie; thence reinstated power to the system with the battery master. At this point I did not observe any smoke or any smells that would indicate an electrical fire. after reinstating power; I slowly added avionics items back into the system. After some troubleshooting we were able to regain essential equipment within the airplane. on board we regained the functionality of the com2 radio; audio panel; and transponder. After regaining communications we [requested priority handling] with approach and continued inbound to land at the ZZZ1 airport on runway XX.After post-flight examination of the aircraft the mechanics determined that the cause of the in-fight electrical smoke was due to a faulty avionics master switch. The problematic master switch had a distinct odor consistent with high temperatures and the melting of plastic around the unit. in the future; to help prevent a similar occurrence; I suggest that during 100-hour and annual inspections; the avionics master switch is inspected for signs of wear attributed to high temperatures to help prevent failures in the future.