OT wiring explanation

[joesatch]

Can someone tell me what the 4 ohm wire from this OT is doing in this circuit? I will use this OT and wire an internal speaker to the 8 ohm lead (which can be taken over by plugging in an external 8 ohm cab via 12a switched jack). Where does the 4 ohm lead come into play? I wont use the 2 ohm lead either (originally wired to a line out circuit)

[joesatch]

it looks like when an external speaker is plugged in,  the jack uses the 4 ohm lead (for the internal 8ohm speaker and the external 8 ohm speaker connected in parallel). So the internal speaker is still on when an ext 8 ohm cab is connected.

[sluckey]

 Correct. also notice that there has to be something plugged into the main jack in order to use the ext jack.