and if the cel light does illuminate its not because the cats were removed it would be because you either have bad sensors or a rich or lean condition pulling codes will tell you what the problem is. the reason i say this is sometimes when you remove the o2 sensors especially if the have some age on them they actually will break or not work properly upon reinstallation so don't panic if you get a cel light just pull codes and go from there and if you have over 70,000 miles on those o2 sensors i would replace them anyways but thats your decision to make usually life expectancy for 1995 mustang o2 sensors are 90,000-100,000 miles..