MX-3.com

Just wondering, where is this located at?
From what I understand, the ATX to MTX swap can be done and you can still keep the ATX computer. Or you can disconnect it. Doesnt matter, but I think I may have disconnected the Fuel System relay (located by the ECU on the passenger side) by accident thinking it was my ATX computer.

You don't even need to unplug it to do an mtx swap.

If I remember correctly, the atx ecm is in front of the engine ecm, if you're looking from inside the car at the dash.

ATX-MTX is quite possible, but you will need to keep the ATX ECM in the car, and plugged in, for it to start. You will also have to jumper one of the connectors that go the ATX itself. Oh, I answered your question on that in another topic...
Jumping that wire basically tells your ATX ECM you're in park or neutral and allows it to relay the signal to the engine ECM that car can be started. It acts like the clutch pedal sensor on MTX cars, a neutral safety switch. The MTX ECM has this circuitry built into it, the ATX Engine ECM does not, it's in the ATX ECM (If I remember the explanation correctly, that was 6 years ago for me, lol)

Replace your fuel system relay. Leave the ATX ECM alone. Install that jumper. And you should be good to go...

About that jumper, I think you can run those wires to the sensor on the clutch pedal so it'll behave like a typical MTX, starting only in neutral. That and wiring the backup light switch are the only things I never did with my swap. I found it convenient to start the engine without having to get into the car every time. but it allows the car to start in gear, which can be hazardous...