FYI the black wires are 12v for the slide motor, not ground.
Yes indeed CalCruiser. I am glad you brought this up.
There are a few odd exceptions where 12V black is not ground, the macerator in our 2007 production PC being another example. It's wierd.
But the general rules is as follows.
With a Brick & Mortar house, the 120V color code,
WHITE IS GROUNDWith motorhome 120V wiring, the color code is the same,
WHITE IS GROUNDAll vehicle 12v wiring including motorhomes, the color code,
BLACK IS GROUNDDon't confuse black 12V ground from white 120V ground in your PC. It is easy to mix them up because both are present in motorhomes.