Have RV Questions? Ask an RV Mechanic Online.
You can check this by looking at the bulbs if they only have 1 filament then the hook up I would try is red to 12 v positive, white to ground , then you need to figure out which 1 is the taillights from the vehicle and try the green and brown to that one, let me know, Jeff
One more thing, your vehicle plug was probably set up for trailer towing, it may not have a charge line directly from the battery system, be sure what your using for the converter wire is not your tail lights.
I have a workhorse 22 Tiffin Alegro. The AC compressor