Good find Jim!
Odd your prior owner change the gray tank. That is a fair amount of work. That is unless they had some mishap that broke the tank and then when change it they upgraded? Maybe, and mostly likely will never know.
I had a ground out issue on my fresh tank. The wire from the tank sensor up through the floor, (the short section of floor, a whopping 3 to 4") had skinned itself on the steel main camper frame. Presumably from towing vibration. This tricked the sensor to be full all the time.
Having a full fresh tank with no water in it is not a normal event. In order to confirm the issue I jumped a wire from the tank sensor run outside and then inside the entry door direct up to the KB panel. With the jumper in place all was good. So the only thing left was the actual wire. I never could find where it was skinned making contact but I just abandoned it and pulled a new wire up through the floor. This time inside a piece of 1/4 plastic tubing to help protect it.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
Google Custom Search For Sunline Owners Club