Typically the gurgling is due to the bubbling in the glycol reservoir due to activity of the pump. If the pump speed is beyond 2, the gurgling is more pronounced. (View Post)
It is a switch for the fridge fan and reports indicate the switch must be on for the three way fridge to work on 12v. https://tab-rv.vanillacommunity.com/discussion/8075/what-is-this-switch-in-my-400 (View Post)