Car subwoofers to amp

Solution
You could connect them in series - parallel which would give you a 4 ohm load. That would have the 2-4ohm woofers connected in parallel and the 1-2 ohm in series with the pair. You won't get the full power of the amp so it may not be worth adding the single woofer in series.
Not in parallel. In series wouldn't blow out the amp. Generally, you want the load to have a higher impedance than / the same impedance as the source.
 
You could connect them in series - parallel which would give you a 4 ohm load. That would have the 2-4ohm woofers connected in parallel and the 1-2 ohm in series with the pair. You won't get the full power of the amp so it may not be worth adding the single woofer in series.
 
Solution