How to use the 12CD Player in the trunk?

I picked up a 1997 Bonney with a 12 CD player in the trunk. The unit is a Electronics 12disk by GM. Their is no info on how to work this unit. The car came with a cassete player,AM/FM, Equalliser and clock. It looks to be a unit installed by GM.
Any help would be great.
Thanks

The unit was probably left from the last owner. The HU your talking about doesnt have an input for the disk changer. Unless its been bolted in with GM printed on it I dont think it would be a stock changer. Go to best buy or circuit city or something and they can tell you about it.