I wasn't aware that Honda had a factory CD player in '89....

It's an interesting configuration...the am/fm cassette deck is all in one, but the cd player is a separate unit mounted underneath. Probably one of the earliest factory CD units. It's clearly marked Honda CD though, and when you insert the cd the radio switches off (until it spits the CD back out, then the radio comes back on).
I guess what I'm really wondering is how to integrate a new aftermarket cd deck into the system, because I have a lot of my vinyl recorded on cassettes and would prefer to keep the cassette deck in the car.
May have to just take the unit out and have a look at how it's hooked into the rest of the system.