Looking again at the computer schematic, most items relate to an Auto trans and this vehicle has a Dodge NV4500HD.
So, what do I do about the water/fuel sensor (hook direct to a ign source & dash light)?
Yes, I believe that would work. The other option is to eliminate it by replacing the filter with one that has just a water drain. I think I have that listed in one of the FAQ threads.
What about the "Wait to start" curcuit and "Intake air temp" circuit?
These were monitored by the computer on the fender well. They sensed switches and probe sensors and responded by triggering the proper relays.
Also, do I need to deal with the Speed Control circuit?
I think that either went to the electronic speedometer from the computer or was incoming from the transmission. I'm not totally sure on this item. I think the 94 and up had an engine speed control that actually controlled the engine speed by the computer but that is a bit too new for me. The 94 or 98 (?? years) accelerator was "fly by wire"??
What's the ASD relay circuit and how do I address it? Lastly, do I just connect the heater relays to a 12volt source? Ign or Batt?
The ASD is the automatic shut down relay which was also on the fender well.
One side went to the run side of the ignition and the other side, both small terminals went
to the control circuit side one to the ignition run side and the other to ground. The other half controlled positive side voltage going to the side terminal of the injection pump's shut off solenoid. When you turned the ignition key it triggered the relay and puts 12 volts to the solenoid through a fusible link wire. For the grid heaters you can use a Ford style single pole normally open starter relay (fender well mounted) and wire the control side to a push button. Wire the control side hot under the hood and have it so the wire coming through the firewall and going to the push button switch is the grounding lead. That way if it should ever rub through it won't set you vehicle on fire. All added under hood relays should be wired in this manner whenever possible or have fuses.