O2 sensor connectors, which are front and rear?

[1998rollover]

I need to verify that some un-keyed aftermarket O2 sensors are connected to the right places on a 98 Mountaineer. Would be no problem if the sensors were OE type with tabs on the connectors so they only fit the plug they're supposed to.

There's blue plugs and green plugs on the wiring harness. Which are the front and which are the rear?

 

[Turdle]

I believe the green are upstream and the blue are the downstream connectors.

In this picture I am removing the downstream sensor, notice the blue connector to the left is disconnected.

The picture is from this thread.

http://www.explorerforum.com/forums/showthread.php?t=209770

 

[1998rollover]

Which blue to the passenger side? The way the guy who worked on this did things, I wouldn't be surprised if he got them swapped.