RV Repair: wiring?, air cond, thick wire

Question
2004 dutchman classic 5th whl. no power to- 12v lights, air cond. , fridge. the slides and jack have power so do the a/c outlets.

Answer
I assume you mean the travel lights (running, brake, etc.) when you say 12v lights.  These campers have a very thick wire for the lights.  Like arond an 8ga.  Find your ground wire from the lights, at the connector, and jump this wire to a clean spot on your frame.  then see if all the non working stuff comes on.  If so, it is a ground wire somewhere.  just tap into this wire and reground.