I'm going to recommend you find a clean level area and some opened up cardboard boxes (say from a full sized refrigerator) and slide under your camper.
Bring a flashlight.
If you don't have the glacier package, all of the tanks and wiring will be there to see. The grey and black tanks will be made from the same material, but the black tank is significantly smaller.
On the side of all 3 tanks will be 4 fine wires attached to brass screws arranged vertically. The bottom most screw is the common.
Check that all 12 wires are safely secured and that the harnesses are out of harm's way.
I would be willing to bet that you've got a bad common connection to the grey tank. Pinched wire ort poor connection. Look for irrational splices, dangling wire(s) or anything that is not smooth.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!