Need help hooking up ewc unit

[needhvachelp]

New (to me) house and the hvac wiring is a bit of a mess. I'd like to give this a shot before calling in an hvac tech. Here is the current setup:

pane furnace PG8JAA/MAA
EWC-ST-3C
3 dampers
3 thermostats (only the main floor thermostat does anything, 2 round Honeywell thermostats don't work/aren't hooked up)

this is the state I found the system in:
- two white wires coming out of the furnace. One I suspect is going to the main floor thermostat. The other one is in a bundle on the floor.
- the 24V power supply is disconnected from the EWC

questions:
- I have a 24V wire coming off of the furnance (on the same jbox as the electrical turn off for the furnance). I can't tell where it runs. What is that for?
- How do I verify the EWC is functional? The fuse looks slighly yellow in one corner. What is the minimum I can do to verify it is functional?


I can read schedmatics and wiring diagrams, but this type of project is a first to me. Any help is appreciated.

[Paul Z.]

Call office at 1-800-446-3110 x490 and I will go over the board with you.