i mixed up the front and rear 02 sensors on my 97. How do i know which one goes where they both plug into both of the harness'. I know one is heated and one isnt but is there a way to visually tell, or is there a model number on it some where ?

 

Downstream rear O2 after the cat is a 4-wire sensor. Front two O2 sensors on the Y-pipe are 3-wire sensors.

 

both of mine are only 3 wires . And they both look exactly the same.. The wiring included thats why im confused. I should also mention i am fedspec.