The lights and all control functions of your refrigerator are powered by 12V-dc from the RV battery/12V system. My guess given the limited description you provided is that the problem is in the 12V
supply, not the refrigerator at this point. Without a working 12v
supply the refrigerator will not run in either electrical or propane mode and the lights will not be illuminated.
First check the 12v
fuses located in the power panel. If all are good, then the next place to inspect is the control board on the back of the refrigerator itself. There are one (maybe two) blade type fuses on the control board and one glass tube type.
The board you seek is under a black cover and the sample board shown here has two glass tube fuses: