Optimus 120-2154 - Manual (Page 6)

4 Ohms. Your local RadioShack store carries a full line of
speakers.
You must connect the GROUND, +12V TO IGNITION, and +12V TO
BATTERY wires first, then make all other connections as
described in the following sections before you plug the harness
with the 14-pin connector into the stereo. If you do not make
connections in the order shown, damage to the stereo is
possible if any wire connections are made incorrectly.
You must connect a separate wire to each speaker terminal as
described in the following procedure. Do not use a common wire
or chassis ground for any speaker connection.
Note: The wires in the wiring harness have the following colors and
labels.
(Black) - Ground
(Red) - +12V to Ignition
(Yellow) - +12V to Battery
(Blue/White) - AMP Remote Turn on 500 mA MAX
(White) - Front Left Speaker (+)
(White/Black) - Front Left Speaker (-)
(Gray) - Front Right Speaker (+)
(Gray/Black) - Front Right Speaker (-)
(Green) - Rear Left Speaker (+)
(Green/Black) - Rear Left Speaker (-)
(Violet) - Rear Right Speaker (+)
(Violet/Black) - Rear Right Speaker (-)
Using an Adapter Harness
If you are replacing an existing stereo, or if your vehicle has been
factory-wired for autosound components, you might be able to use an
adapter harness to connect the power and speakers. RadioShack stores sell
adapter harnesses for most vehicles.
Follow the directions that come with the adapter harness to temporarily
connect the ground, power, optional components, and speakers. Then go to
"Connecting the Antenna" below.
Connecting Ground, Power, and Optional Components
Follow these steps to connect the harness with the 14-pin connector to
ground, primary and memory backup power, and optional components.