I found the same issue with our 990. I removed the sink and very carefully drilled a 1 inch hole next to the original that was full of wires. There are wires all in that wall.
be careful not to hit anything if you drill.
I still couldn't get to the hole very well so I poked some string down in the wall and was able, using a vacuum, to suck the string through. I then pull several strings through and pulled the wire I wanted. I still have several of the strings hanging out of the hole under the sink in case I need to pull another wire in the future.
As far as solar our 990 was pre-wired for solar. Your 811 should be also. The ends of the wires were capped and rolled up in the cavity behind our radio in the kitchen cabinets. The newer AFs I believe should be in the wall behind the sink.
