First make sure you know which of the two motor wires was connected to the plus terminal of the battery and label the wire using a piece of tape or tie a simple knot in it. Remove the paper fastener connections and brown sleeves leaving the bare wires exposed.
Connect the solar panel to the motor wires making sure to twist together the bare red solar panel wire with the bare plus wire which you labeled in the previous step.
Twist together the black solar panel wire with the remaining motor wire.
Replace the brown sleeves and paper fastener connections. The sleeves will be tighter than before because of the extra wires inside.
Hold the solar panel onto the chassis with an elastic band.
Lead the red solar panel connection to the + side of the battery (the + of the battery has the bump or cap on the end!). Lead the black solar panel wire to the - (minus) side of the battery (flat end).