Ok so I'm having a weird issue....

Turn the car on, everything works as expected.

Turn it OFF, take the key out, and the CEL and Air Bag light are dimmly light! If I switch on anything that SHOULD work when the key is in the ON position, it works! So for some reason, the car is staying on, even though it's switched OFF.

Any ideas?

 

Disconnect the ECU connectors, see if the power goes away.

 

Just tried this.

It worked! As soon a I removed the bottom connector, lights went off. I plugged it back in, lights STILL off. But after I cycle the key on and back off, they lights stay dimmly on, have to unplug bottom ECU connector to get them to go off.

What does this mean?

 

It means that something that is connected to the MS3 is receiving power when it shouldn't.

Start by disconnecting whatever is on the bottom connector, one by one to find which one is causing your issue.

 

My MS3 is in a box! Not installed at all. This is a stock wiring harness in the car.

 

Solved.

So the Airbag light was on, as I said. Code was 49, which is the code for "the switch to disable the passengers airbag is having a bad day". That was because that switch was not plugged in.

So plugged it in, problem solved. No idea why/how the airbag system would keep the car on.... But that was it.