I agree - the Solar wiring loops behind the front panel - and then terminates behind the power cord reel in the basement. You may need to remove the black plastic panel behind the power cord real to find the wires.
The positive wire is tie-wrapped to a bundle of wires behind this black panel.
The white ground wire was ganged together to the frame behind the wiring "cluster" located behind the power cord reel.
It's important to locate the white ground wire and separate it from the bundle to wire directly to the solar controller - or most likely the solar controller will not work correctly.
I purchased most all of my equipment from AM Solar. They tend to be pricey - but the follow-up service is exceptional - and always returned phone calls to offer advice and to answer questions. Clearly there are less expensive avenues - but I wanted a go to place for advice - and AM Solar was great - and all of their gear was top shelf.
I installed three (3) 160 watt panels - and on a sunny day will generate about 20 amps. The wire gauge Newmar installed limits the amperage available. I also have a portable 160 watt panel that I use occasionally.