What does your key look like? Mine reads "PATS" and on the other side has what appears to be an identifier code. I suspect that code is the key to figuring out which you have. Another item that may help is the build date of your car. Mine was born in 04/98. Hope this helps.
One other idea- I was reading a thread where someone was asking about getting in to the repo business. Someone who worked at a dealership mentioned how they cut new keys all the time for this reason. Have you VIN handy and call the service department. Call asking for a price for a new key. After they give you the price ask if it is PATS or II. This will be the quickest way I think.
for those who purchased their 96-98 mustangs new, what did you receive from the dealer? 2 keys? are they both identical? I keep reading about a master key that is red but not sure what this is.
unfortunately i purchased the car used with 1 working key. i would like to get a second key working w/o having to pay the dealer to program it.