Valve both cylinders out.......CLOSE the OPD valves
Disconnect the ACME Green Nuts from both cylinders
Open one of the stove top burner knobs to empty line...close it
Connect ONE of the ACME Green Nuts to cylinder making sure it is Tight
Turn auto changeover lever to that cylinder
SLOWLY open Cylinder OPD Service Valve....should hear a click and Red/Green Indicator should turn GREEN
If it doesn't then Pigtail is faulty
Try the other side.....same steps
Having AC Power or DC Power IS NOT required on trailer with propane cylinders.
No Shutoff Solenoids.....Some older MHs did have them/Newer no longer----some Class Cs have them due to remote controls
BUT NOT on trailers
Propane system is MANUAL...up to the appliances. Appliances use DC