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These can be wired in many different ways, and those vary with the particular model of furnace, and if it has a communicating thermostat or a more common standard non communicating thermostat, it can take hours to sort this out.
The primary issues are the blower must be running whenever the water solenoid valve on the humidifier is energized AND the outside air temperature should be below 60F (lacking that you can have the humidifier running in cooling mode).
Your offer will not cover that much work on my end, let me know if you are interested in additional service offer that will cover 2 hours of my time or not.
We can go from there or I can opt out to a host of other HVAC experts on the site.