I posted this question on r/homeautomation but it keeps getting downvoted. I'm guessing it wasn't the right place to ask.

So basically, I want to add a C-wire to power an "ecobee3 lite". The furnace is a PSG4000 WOOD/ELECTRIC and the control board doesn't have any of the standard wiring designations (R,W,Y,C...etc).

I want the ecobee to control the electric heat of the furnace, and there are currently 2 wires (R/W) running to the mercury thermostat that I'm replacing.

The ecobee tech support pointed me to an adapter called a "Fast-Stat Common Maker" which seems like it would work, but their install instructions still direct you to tap into the "C" terminal at the furnace which I can't identify.

Here is a wiring diagram of my furnace: Wiring Diagram

Is there anywhere I can connect a wire to act like a "C" terminal? I noticed the blower has a "common" wire coming from the "E" terminal on the power block. Can I just add a wire to that terminal?

Or can I connect a wire to one of the 24V transformers? Or will it draw too much power?

Alternatively, if I do find a proper "C" terminal, could I just run a third wire to the thermostat that comes directly from there, removing the need for the FAST-STAT?