Wiring is now complete! Make sure the jack nut is tightened down securely. Carefully install the sheet metal cover back in place using the four small screws. Insert the batteries, and test out the amp. With nothing plugged into the newly added jack, sound should come out of the Pignose speaker as usual.
Now open the amp case, and plug a 1/4" audio cord into the new jack. Plug the other end into an 8ohm speaker cabinet - any size - and try it out. Good luck, and enjoy.
The attached schematic diagram shows what we just did.