Just got a V6 1999 automatic convertable mustang. Looking to replace 4 O2 sensors . Want to get Bosch waiting until they open. Having difficulty getting exact part numbers? Does the same sensor go on all 4 places? Rock auto description was confusing with one goes left up and downstream . One just upstream. Cannot seem to get straight answer?

 

I can see how that is confusing. If you look at the other sensors they are both left and right per stream. As long as you get two of the correct up and down you will be fine. All the sensors are the same size. So go with:
2x15717 Up
2x15716 down

By the way, I am running Boschs in my truck and they seem to be doing well so far. Solid choice. I did manage to hunt down original sensors for my 02 Mustang. May be worth the effort if interested, though I had to pay a little extra for them.
Motorcraft
dy-1093 Down
dy-832 up

 

I called Bosch this morning they said 3 of them are the same 15717 And the downstream left is the one 15716. I figured I would go to the tech professionals.

 

Wow, that isn't confusing at all, haha.

Definitely go with what they said, what the heck do I know

 

I hear ya ! I was confused as hell... nothing beats the confusion of my wife's chevy sonic though!!!