Take the Left/Front/Positive wire coming out of the radio and twist it together with the same wire going to the tweeter, as well as the one going to the front speaker.

Then, use a wire cap to secure the wires together. Wrap the wire cap and wires with electrical tape.

Do the same for the Left/Front/Negative, as well as the Right/Front/Positive and Right/Front/Negative wires.

You can alternatively solder the connections together, or use crimp connectors.

I used wire caps to to connect everything and to make sure it worked, with the intent to solder the connections later. But after verifying that the speakers worked... Well... They worked, so I didn't bother.