the MIl goes between the O2 sensor and the factory harness, you unplug the )2sensor and the plug in the MIL then plau the factory harness into the other side of the MIL to complete the circuit to allow the MIL to feed the computer with lies and make it think the cats are still there.does that make sense?

- is the factory harness
= is the MIL
O is the O2 sensor

should look like this...

-=O