I recently bought a used boat and my tachometer/speedometer was not working (stuck at 6000rpm). I understand that Tach damage can be caused by electrical transients disconnecting the battery with the engine running. I bring this up because it has happened once while the boat was running. I suddenly lost power, shutting down my fish finder, gas gauge, and caused a sputter in the motor. Battery terminals are not loose and battery switch was in the on postion. Everything returned to normal once I switched the battery to off and back on. What can cause my sudden power lost and how to fix? Is my Tach and speedometer gone and need replacement?