PA-31 Navajo/Chieftan/Mojave/T1040
Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Flight Crew Last 90 Days 200; Flight Crew Total 31700; Flight Crew Type 9000
Confusion; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Diverted; General Maintenance Action
Aircraft; Weather
I was flying IFR. The copilot's Heading (HDG) indicator had shown wild precession on this flight. We were headed north; my HSI indicated north. The center said; ' I see you are in a left turn; are you still proceeding to your destination?'  I said 'yes;' they gave us a turn to a heading. My HSI stayed on north; the copilot's HDG indicator was unreliable. At this time we discovered by our GPS that we had made a 180 degree turn without realizing it. Knowing that the weather was VFR in the alternate but not at our filed destination; we used our GPS for heading direction and proceeded to our alternate. We had lost use of my HSI; my flight director; autopilot due to a series of electronic failures. We proceeded to the alternate; landed in visual conditions; and turned the plane over to maintenance for repairs.
The reporter stated they determined after the flight that the alternator powering the affected equipment was intermittently malfunctioning.
A PA-31T corporate pilot reported his aircraft made a 180 degree turn while IMC after a faulty alternator output affected the Captain's HSI; Flight Director and autopilot. GPS heading was flown to the VMC alternate airport.