Wiring Car Stereo to Mono Speaker, How?

My old car vintage car originally had a mono radio connected to a single mono speaker. The previous owner changed the radio to a period-correct stereo radio (Becker Europa II) and added portable stereo speaker that are now gone. I now want to connect the stereo radio to 2 tweeters and one full range speaker and though to use a BOSS CE102 amp. I can feed the high signal from the radio directly into this amp but need help with wiring the output. The amp has a built-in selectable cross-over (LPF,FULL,HPF). See schematic below. How do I split/combine the output signals?
The tweeters are a pair of BOSS TW17 mini-dome (total power: 200W) and the single speaker is rated at 20W (rms).

Had to learn how to attach a pix - hope this works now.

If one of the connections of the mono speaker is connected to the chassis of the vehicle, DO NOT do the following.

Connect the positive full range speaker wire to the left positive connection on the amp. Connect the negative full range speaker wire to the right negative connection of the amplifier. Play the amp and make sure the speaker plays. Balance the radio to the left channel only, does the speaker still play? Then balance it to the right, does the speaker still play? If yes to both questions, connect the left tweeter to the left channel of the amp and the right tweeter to the right channel of the amp.

If no to either or both questions, post your results here.

Thanks for your quick reply. I'll try to do what you suggest next week when I am back home.
Also want to try again to post the amp schematic. I have no clue why it doesn't work since the size is below the limit and the extension is .jpg. Perhaps I mod can help?

Finally it worked.
So, to verify what you what you are suggesting is to hook up the single speaker in parallel to the two tweeters. I'll post my results next week.

Took a little longer than I expected to check this out but here is what I found out.
1. Connected full range speaker+ to +L on amp and speaker- to -R on amp.
Speaker plays.
2. Unfortunately the old stereo radio does not have a left-right speaker balance function so I could not check whether the speaker still plays under these conditions.
Shall I now try to wire the two tweeters in as you suggested?
Anything else I should test?
Thanks for all your help!

You really need to disconnect the input wires one channel at a time to make sure that the mono speaker plays with each channel playing.

Sorry "iaai", but I am a newb and don't quite understand what I am supposed to do.
I have connected the radio out wires as shown in the diagram below (high impedance input on amp) and then connected the amp out wires as you asked me to do. The single speaker played but I could not balance the radio to the left channel only, or the right channel only and test whether it still plays, because the radio doesn't have that function.
What next??