Where do I plug in the front o2 sensor? There are three plugs I see that match up...

1. By the firewall with the emission stuff
2. Comes out of the harness with the coolant temp sensor and all those plugs on the passenger side of the motor (I think the CAS and stuff?)
3. Comes out of the harness with just the MAFS plug.

I doubt its #1...I tried #2 and #3 but I can't really tell the difference.

Any help would be appreciated...thanks!