[pairodice]

I have converted the AC system to 24-volt thermostat and relays so I would need to wire in an interim relay to make the 24 to 12-volt jump to the AH unit. Thank you Richard! I understand what the switches at the microwave panel do and they are working properly as I can turn on the 110v electric (I only have 30amp in the building) and it works fine.
I did test the continuity and cannot find the wire for the life of me…
W1 = heat on the TStat which is a yellow/black wire on the rear TStat and a yellow wire on the front TStat.

Does the yellow (W1 from TStat) go directly to the AquaHot unit or does it go to the SCS Basement unit board first? 
I have been trying to check continuity using a 20’ 18ga wire from the rear AC (and the front AC) down to the Aquahot and also to the AC units but cannot get any tone out of it. 
I know the continuity tester and wire is good because when I touch the ends together I get a tone (I know enough to know how to do this part)… I’m baffled as to where these wires from the TStat end up.  I know the smaller gauge wires got directly to the SCS AC in a bundle that is twisted into the side of the AC unit via a bung of sorts to make the connections and they are working fine to run the AC units. 
The pictures attached are the AH board/labels with the yellow/black for rear heat and yellow/red for front heat…; and the original 12-volt TStat; the new TStat is an Ecobee with two stages for the AC.

Adrian