Optimus 120-1998 - Manual (Page 7)

7. Reconnect the cable to the vehicle battery's negative (-) terminal.
REMOVING THE STEREO FROM THE DASH
1. Disconnect the cable from the vehicle battery's negative (-) terminal.
2. Remove the metal strap attached to the back of the stereo.
3. Insert both of the provided keys into the slots at the lower left and
right sides of the stereo. Then slide the stereo out of the dash.
4. Remove the keys from the slots by pressing the latches either below
the keys or on the lower left and right sides of the stereo.
5. Disconnect the wiring harness and the antenna.
6. Reconnect the cable to the vehicle battery's negative (-) terminal.