I'm looking for a wire that goes from the stock main harness at the ECU directly to the engine bay to use for EBC in my MS3. I don't use the MAF harness, so I'm wondering if any of those wires would work; especially since they would be in a pretty good location for it. I also forget just how many wires I need for EBC, it's just one to power, and ECU switches to ground, right?

 

it would work, yes.

I send a triggered ground through my AFM harness to power a relay.

 

Yes you can use it. Fortunately, the MAF works with 12V, not 5V, so you have your 12 volts ready and the "ground" for the EBC (ie the signal wire of the MAF) going back to the stock harness.

 

I'm using the maf signal wire to drive my EBC solenoid, it hasn't melted yet (94, using the blue 12v connector for power (the thing you use to hook up power for a timing light)