It'll be a wire, the motor, a slipped gear, bent arm or a piece of toast.
Failing that, take it to an electronics repair shop ( I'd say TV and VCR repair, but they don't seem to exist anymore.
![Laughing :lol:](./images/smilies/icon_lol.gif)
Your replacement head unit probably has an ISO connector whereas the car has the Honda specific connector - not sure 5th gens ever came with the ISO connector (the jap manufacturers were among the last to introduce them). You can buy plug in convertors easy and cheap enough.