question about speakers in a 89 'stang lx

i'm helping my sister's boyfriend put in some speakers in his 'stang this weekend. only problem is that he lives in CO and i don't have a chance to look at the car before we get up there. the second problem is that he lives in a TINY town. i sort of need to know all the stuff before we go up there. my only question is, for the inside speakers do i need a speaker harness or anything like that? I know some cars have a weird harness to connect the speakers to the factory wiring. he is not planning on amping these as of now so i know he is just gonna run them off the deck and use the factory wires.

you could always pigtail off of the factory wires with connectors that match the new speakers if they are different from what is in there...that way if he decides to sell the car later and wants to put the old speakers back in, he can do that as well without having to re-wire again...

ooh thanks the idea and the help. i'll probably just do that.