Unplug the frige. Then find the connection for the 120v heater. Unplug that and set the meter to ohms. Put one lead in the plug and put other on the pipe. If there is a short there, it will show 0 ohms. The heater itself should show some sort of resistance somewhere between 350 and 600 or so. May be higher.
2000 Dodge Dakota
1406 Jayco Dual axle