Just played hide and seek with the solar pre-wiring in my 990... First, look for a bundle under the sink against the cab-over wall. If not there, remove the tank level check panel; mine were there. I had to call Northwood...
Should be two sets, one from the roof and one from the battery box, all bundled together. Both should be labeled and taped together in pos/neg pairs.
Up top, look for the SAE two-prong plug. It will be somewhat buried in DiCor.
Good luck; let us know how it goes
BBF