Extension cabinet and amp impedance question

[TheGuildedAge]

If my amp has an 8 ohm speaker in it, and a tap for 4 ohms, do I run the amp's speaker out of the 4 and then the 8 out to my cabinet?

I want to turn y 1x12 combo into a 1x12 combo and a 1x12 extension cab.

 

[walterw]

what amp?

in theory no, you don't run different speakers out of different transformer taps at the same time, but some amps are wired up with switching jacks and/or confusing labeling, to where the 8Ω internal speaker stays where it is and plugging another 8Ω speaker into a "4Ω" jack is actually switching both speakers over to the 4Ω transformer tap.

 

[Tone_Terrific]

some are not labeled at all.
Some have internal swithching as WW notes.
Some have impedance dedicated output jacks.
Some have switches that pick different imp taps on selected output jacks or pairs.
It is truly crazy.
Pulling the chassis to check the config should never be necessary but it can be required due to poor or lacking labels.