HELP - Tune up

Please help ASAP
98 mustang v- 6
replaced plugs and wires today
car running AWFUL - was fine before
went back to O-reilly's - they had sold me 104's instead of 105's (plugs)
replaced new ones and car running BAD!!! Missing - check engine light came on -
NOTHING else was done to car except plugs and wires - all plugs firing....

Are you sure you got the wires on in the right order?

here is the firing order of the pistons on your block,
http://www.allfordmustangs.com/techarticles/images/mustang94-98_v6_f6.jpg

Make sure you have them hooked up in the right order, if you dont have a manual on your car... you should probably get one. They're pretty handy for stuff like this...