You can just follow the circuitry very careful and you will be able to see the fuse. You can employ your sense of smell and sight to find the blown out fuse.
does a water heater require a ground wire?
Right under the throttle cover.
no
take negative off battery for 30 minutes and clean the Throttle Body
try switching the 2 heater hoses around, they may be backwards
Take the hoses of and run water backwards & forward through it.
This will not effect the engine in any way
The fuse for the mixture heater wires for a 1998 Nissan D21 for cylinder is an electrical device which interrupts the flow of current when there is overloading.
yes
check the fuse or the ground on the heater
Yes, if you get them backwards, you'll have AC instead of heat.....Just kidding. It doesn't make any difference.
on heater core inlet tube next to throttle body