with the bat disconnected, that shows the problem isn't in the wiring or the converter. not much left except the battery.
the tent lift motor may need the extra power provided by a battery. the converter may not be sized to carry the motor by itself.
as suggested by others, u do need a volt meter. (used mine yesterday after the alternator went out on the tow viehicle). u can varify the proper wire to connect to the battery by observing if the meter shows +12 or -12 when connected to the leads to the battery (with the battery disconnected and the trailer on shore power). make the same measurements on the battery and match + to + when connecting the trailer wires to the battery. i should know the color code but don't. if i have any doubt, i always do the voltmeter check. there is a good possibility that the fuse at the battery is located on the posative lead. a wire that bolts directly to the frame is negative.
batteries are strange anamils; they can be bad right off the shelf. my battery usually starts running hot (very warm) to the touch when one of the cell goes bad. because the converter is having to supply more current to try and bring it back to normal, it is possible to blow a fuse on the converter. i have seen schematics that show a reverse polarity fuse on one. haven't looked at mine to see if it has one or not.
let us know what u actually find.