I noticed a few times now my voltage is below 12V while idling, and once my batteries were too dead to fire the truck. When it is happening the voltage will stay low even when the engine and ambient temps are warm. I unplugged the relay on the passenger side battery box which I believe sends power to the grid heater solenoid. Immediately my voltage jumped from 11.9 to 12.7. I’m guessing the solenoid is stuck on and need replaced. Tried a different relay which didn’t help. Am I on the right track? What else could that relay control?