Here we go. We have a 2005 Bounder, gas, workhorse chassis. When not connected to shore power we do not have 12vdc in the coach. Just replaced the coach batteries, originals were two 12v deep cycle ba...
I go with the first reply. You already have a major cable not yet connected. Some RV 's need a connected battery for the 12 volt circuit to work.
With little knowledge you might connect the batteries backwords or cause an accidental short.
Best answer for you is to get an expert to connect the cables and watch what he is doing. Reading the manuals may be better than paying for a few hours help since most will not remember what was said by their next trip out.