Hey
I am not sure where you get your info from.
You only get electrical load shedding on the 767 during fuel jettison when you only have 1 "one" electrcal sourse. eg when testing the system on the ground external power or APU supply.
For the life of me I cannot understand why you would worry about inline water heaters when you are in a situation requiring fuel jettison.
Landing lights some but not all are powered from the essentials bus...not load shed.
Hope this helps