Using Audio Jack Switches as Paralell/Series toggle? (guitar amp and cabinets)
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Your three options with your kit.







simulate this circuit

Figure 2. Single or series connection using switched jacks. The inserted plug makes contact with the free arrow while it opens the contact with the touching arrow.



Figure 3. A switched jack socket with NC switch contacts clearly visible in the forground.

How it works:


Connecting Speaker 1 will give the amplifier connection to the tip and the ground connection will be through the normally closed (NC) contact of the second jack.
Connecting Speaker 2 will open the tip contact, disconnect the ground and the first speaker will now be in series with the second.


The circuit should be as fool-proof as the original jack. There is no additional risk of short-circuits. (There is and was a risk if it is possible for the jack tip to short between tip and sleeve during insertion.)




  Would it be possible to execute this using a vintage-style female jack as well, like pictured here?




Figure 4. OP's vintage jack.

No. Look at your image. There are no switching contacts. You need one switching contact on the tip at least.