If the battery is just behind the tongue the charger should be just inside the trailer under the couch or what ever is just inside the trailer. Once located check for AC power to the convertor at the AC plug with a meter or any AC item you can plug into the receptacle. If there is power check the fuses on the convertor itself. If the fuses are good check the output voltage of the convertor with a DC volt meter or test light with the battery disconnected. If everything checks out to that point go to the battery itself and again check the voltage on the cables leading to the battery. You should see about 14 volts open circuit at the convertor output and at the battery cables. If everything checks out OK to this point connect the battery and check the voltage on the battery. It may be very low but leave it charging for an hour or so and recheck. It should have increased. If not the battery may be shorted internally.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles