For the heater, just wire it to the old heater wire. The old heater is the bulge on the steel fuel line going from the lift pump up to the filter header. Just swap the wires.
For the WIF sensor, I did some heavy research on this recently. There is a module that this connects to which is basically a solid state relay. When water hits the sensor, it grounds, but can only conduct a very small amount of current. As in, enough to throw a solid state relay, but not enough to power the light in the dash. The relay then would then send 12v to the dash light. I know one of the wires on your old one is 12v key on, can't remember the other two. This fellow
http://www.intellidog.com/dieselmann/filter.htm has the module for $35. Part number is E8TZ-9S281-A.
Another member posted 1989 wiring diagrams (so, using the new header and WIF system) here
http://www.oilburners.net/forums/showthread.php?44434-Wiring-Diagrams-(1989)
Look at the one called "Instrument cluster" and you will see something called "Fuel Water SW" That's the module I'm talking about. And that's how it's wired up. That's how I'm going to try it on mine when I get home this winter, only I'm going to scout the salvage yards to see if I can snag one cheaper. I'm really ticked off that I didn't know about it enough to grab the one on the truck I got the header from
I did the header swap myself, and personally, I just plugged the vacuum sensor hole. I still have it and might end up wiring it to an idiot light, but I'm also putting on a fuel pressure gauge in the near future which kind of eliminates the need for it. If you want to use the factoury sensor, then just hook a wire to the vacuum sensor, run it to a light somewhere on the dash, run keyed hot to that light, and use the wire from the sensor as the ground. Bingo, when the fuel pressure drops to a vacuum, your indicator will light up.
