There's supposed to be two on some cars, I'm not sure which of our cars but my 97 aspire is a 2 oxy sensor car. The 1st one is located in front of the engine on the exhaust manifold down low, but before the down pipe. This is a "single" wire type. The second one is supposed to be right after the cat, (My car didn't have the exhaust system when I got it) but I have what's left of the wires. Speaking of wires, this second sensor is a "four" wire, heated type. It actually gets "pre" heated cause they aren't read till they reach about 600 degrees. I believe the purpose of that second one, is to sample exhaust AFTER the cat has had a chance to clean it up some......... Ok went out to the garage and got the book and the wiring diagrams say:
1988-89 festy (carb) 1 sensor w/ single wire
1989-93 festy (FI) 1 sensor w/ single wire
1994-95 aspire 1 sensor, single wire w/shield wire
1996-1997 aspire 1 sensor w/ single wire, and 1 sensor w/ 4 wires.
Sorry, don't have anything after that for our Aussi Gang.