Valerka,
on your 1992 there is only one o2 sensor. If you look at the back of the engine where the exhaust pipe goes down (down pipe), just before it starts going down you will see what looks similar to a spark plug. That is what you are looking for. Be sure to put anti-sieze (usually it'* already applied by the manufacturer) on so the next time it gets changed it'* not too hard.
Good luck,
Martin

If memory serves me right, all series I 3800s have only one o2 sensor. Series II 3800s have two.

Alright finnaly did it, altough I am just wondering if I had to lift the front of the car to do it? Or is it just me?