if you have no power going to your ecu, the ignition (like you said) could be the problem. but if you're getting the correct amount of "clicks" turning the key, and it's turning the engine over... (and let's not forget that it worked before the harness swap) I'd highly doubt it's causing this.


Start tracing wires

one

by

one.

starting at the battery going torwards the ECU.
I don't think the problem is the relay, it's a rare chance that the "new" one you got is bad also. My money is on the ecu/power problem.

So many things wrong at once when they were working before the swap? I'd say it's an engine harness with some issues.