What harness plugs into the ECU? I can’t find anything anywhere about it

 

Heres a video.

 

Depends on which ECM you have, there were 3 options. The ECM is next to the glove box, if you have an early model you might also have the TCM next to the ECM.

Here were the three ECM options, ignore the green check and red X, that's for Uprev tunability.

 

It’s a HUGE plastic connector on the passenger side lock area behind glove box. Looks like this kinda (aftermarket ECU here, but same plug).

 

ECU connector.