You can add a switch to switch between stereo and mono modes using the two jacks. For example, in the Mono position, jack "A" is only used and jack "B" is not, in this position you would be running how ever many ohms your cab is wired for. When switched to the Stereo position, both jacks would be utilized for left and right channels, and the ohm load would double. If currently wired for 8 ohm mono, stereo would be 2 16 ohm loads.
My 2x12 cab is wired like this.
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