My Jade plant seems to be rotting. Large branches are falling off and when I cut them, the interior is wet and dark brown. I have cut back the watering dramatically and water only when my hydrometer gives me the proper moisture level. What can I do to rehabilitate it?
Wet, brown, and stinky tissue inside the branches indicate that the plant has been consumed by root rot; cutting back the water now is like closing the barn door after the horses have escaped. You can't rehabilitate the plant. The best you can hope for is to cut off any green growth that remains, and try to root those cuttings.
In the future, do not water any succulent plant until the soil IN THE BOTTOM OF THE POT is almost completely dry. I'm sure what happened to your unfortunate jade is that, while the top of the soil may have felt dry, the soil closer to the bottom of the pot, which is where the roots were, remained wet.