Is the breaker for the tuner off too? Or was the equipment close to the autopilot's control box or it's compass. Who's autopilot and instrument system do you use? (It could be (or been) a backfeed from the SSB that affected the system if it's integrated with the pilot.

Do you have a separate ground plan for the SSB?
Do you have the Ground for the SSB or the tuneer that is tied-directly into the line from your instruments?

I would recalibrate the compass and the see if it works --- WITHOUT POWERING UP anything on the SSB system.

Then I'd see what I see?