What kind of gas furnace has a water hookup?
Is this a boiler? What is the "make-up-air fan? Is that a combustion air fan in the furnace room or a unitary part of the "furnace"? Most if not all furnaces have their draft inducer and blower motors internally wired in the equipment harness, it is not usually part of the electrical connection, as part of their aga approved status. There is usually one point of connection for line voltage and one point for class 2(thermostat, control). Is the water hookup for a humidifier, or is this a cutoff for a steam boiler? If this is boiler wiring, let the heating guy do it, this is generally not covered by a sparky's liability insurance.