Couple ways to check. Take the black and white leads off the converter then take a multimeter set it to read dc volts plug the trailer into shore power. When you check across the lugs where you removed the cables you should get a 13.5-14V dc reading. If nothing, disconnect cables from battery you should get the same reading there if the battery is good. If battery is good reconnect battery cables then plug in a battery charger and hook charger cables to blk & wht lead from converter. Check your dc lights. This is the process I followed when my converter went out.