What year is your Hornet?
Keystone archives some of the more recent Owners Manuals on their website -- none are model/line specific, but rather generic, basic/general information.
There's also some "Service Tips" videos on the Keystone site which may be helpful. http://www.keystonerv.com/customer-service
Unfortunately, there isn't a "one source" website for appliance & component manuals, so you'll have to go to each manufacturer website. Brands may vary
from year to year, so gather names/brands (model/serial #'s are sometimes also needed) of the items installed in your particular unit.
Here's some examples to get you started:
Water Heater -- Atwood, or Suburban
Oven/Range -- Dometic, or Suburban
Frame, and Slide/slide-out Mechanisms -- Lippert
Toilet -- Dometic/Sealand, or Thetford
Refrigerator -- Atwood, or Dometic, or Norcold
Air Conditioner -- Coleman/Coleman-Mach/Suburban, or Dometic
Awning -- A & E (Dometic)
Furnace -- Atwood, or Suburban
Last, but not least, Keystone plumbing & wiring diagrams aren't available to the public.
Enjoy your new-to-you Hornet, and
to the forum,
Terri, the Chevy co-pilot