I had that very same model.

You do have keyless entry, yes. Also, the electronics that were/are set up
in the Honda stock radio control the keyless entry and the interior lights,
and possibly something else. If the stock radio is still in the vehicle, you
may only need to re-hook that up, and all will be fine. Maybe.

I thought the stock radio was terrible, so I had an installer install an
aftermarket Kenwood deck. The stock radio remained hooked up to the car's
essentials, but was "shoved to the back." That is, the new Kenwood was what
was visible; the stock radio was behind it.