So, you have the pre and post 02 sensors. Now, when you put on the LT's the 02 holes in them need the extensions and plug into the (pre)front 02 plugs right? And the (post) back 02 plugs you just plug in the little 02 simms. Why does the post 02 simms have some circuitry on it?

 

first two questions, answers are yes. not sure about the third ?

 

what do you mean by circuitry? Are you referring to the black rectangle?