I am installing a THX9421 thermostat and a TrueSTEAM humidifier. Pretty easy, until I have conflicting information. The diagram in the TrueSTEAM instructions (p.17) is very simple. R&C to HVAC, 1,2,3 to thermostat and HUM to humidifier. But (1) there are no HUM terminals in the thermostat. Also, p. 15 configuration 1 indicate dip switch 4 should be ON. But, that contradicts p. 21 OPTION 3 - using the IAQ w/fan delay [and then to boot is shows a totally different wiring configuration to both the HVAC and the humidifier! This is not the end -- as the thermostat installation p. 15 shows connection U1 to the humidifier - and then to 24V [so - it makes these the HUM terminals... right?], but there is also another connection (R & C) will be the HVAC R & C? [24v]? Close?