There is a picture in my Tech Album that may help. As noted above, you simply bridge the two 6-volt batteries together by connecting the positive of one to the negative of the other. Now it is the equivalent of a single 12-volt battery.
http://www.trailmanorowners.com/foru...&pictureid=451
I'm not making much sense out of your pictures, but your description seems to say that you have three black wires. Ther\se are
o lights and 12-volt appliancers in the TM
o charge wire from solar panels
o electric jack?
All of these should be connected to the + terminal of the equivalent 12-volt battery.
There should be a white wire (goes to the lights and applianbces in the TM) and a bare wire (goes to chassis). In some newer TMs, I understand that there is only one wire, which is white. Either way, these wires go to the negative of the equivalent 12-volt battery.
Note that with a 12-volt battery, there is no way to connect anything to the center of the battery. This means that you should not connect anything to the middle of the equivalent 12-volt battery. According to your description, you have connected something, and not surprisingly, it doesn't work.
At the end of this season, you might do better to make a pencil-and-paper sketch of the hookup, rather than a photo in which the actual wires are concealed.
Bill