This question is too vague to answer. Year, make, model - power locks? Key-less entry, or keyed entry or both? Quick "vague" answer - mechanic or automotive locksmith.
In my 01 neon LX it's on the left side of dash, on the side, behind a removable panel. I think its #14 (20A)and #16(5A), depending on which problem you have, but look on the inside of removable panel...