It is hard to imagine you only have two red cables going to the battery box area. RED usually means +12VDC. IT could be if you look around you may find a BLACK cable that comes directly from FRAME GROUND.
I would most definitely hand trace those two RED cables and find the one that goes to FRAME GROUND.
My trailer battery has two 'HOT' cables coming from the POS +12VDC terminal of the battery with one going to the CONVERTER +BAT connection and the other one going to a RELAY that is controlled by my SLIDE switch. I also have a third cable going directly to the trailer FRAME GROUND coming from the NEG -12VDC battery connection.
I would be very CAUTIOUS hooking one of those RED CABLES to the NEG -12VDC terminal of the BATTERY. You must 'HAND TRACE' both cables to see where they go first... Grounding a POSITIVE +12VDC RED active cable will short out something else in your RV. Have fun tracing all of that out looking for a blown fuse (or worse) if that happens.
If you do indeed find one of the two RED cables going directly to FRAME GROUND connection then get some BLACK SPRAY PAINT and paint over the red color cable or better yet replace it with a BLACK color cable you can buy at the local Auto parts store with ring terminals on it.
Always fun purchasing a pre-owned RV - You have no idea what the previous owner has done to it.
just my thoughts
Roy Ken
