Line 6 Flextone III, Spider II Speaker Series Modification
This modification will allow you to optionally use the internal speakers in tandem with another cabinet. This mod assumes that you are using 2x8ohm internal speakers and 2x8ohm speakers in the external cabinet. The result is running at 16 ohms.

Bill of Materials

1 single duplex junction box 3 *NL4 Panel Mounts 7 *Dayton Audio 4 Conductor 11 Gauge Speaker Cable 1 Dual NL4 Cabinet Dish 1 NL4 junction cover plate Gauge Female Tab Disconnects 3 NL4 cable mounts 2 Wire nuts

Flextone III XL Mod

Punch out both short-side ends of the junction box. Also punch out one of the long sides. Mount the junction box horizontally between the speakers allowing or more of clearance between the long side of the top of the junction box and the amp chassis. Disconnect the internal speaker wire noting which side came from where and polarity. Re-route the internal wire to the top of the mounted junction box using 1 of the rubber cable sleeve from the Dayton speaker cable for pressure relief. Do your best to insure each wire is as close to the exact same length as possible then cut the wires. Cut a 14 piece of the Dayton speaker wire and remove the rubber jacket. Make twisted pair out of White: Black and Red: Yellow. Twist every 4 inches or so. Put quick disconnects on all ends except one end of the white and red wires. Plug the ends with the quick disconnects to each internal speaker using white and red for +. Route the other ends into each corresponding short end of the junction box using 1 of the rubber cable sleeve from the Dayton speaker cable for pressure relief. Using the wire nuts twist the + internal wire to the corresponding white or red wire. The internal wires go to 1+ and 2+ on the NL4 The wires (Black and Yellow) coming from the internals go to the 1- and 2- on the NL4 junction plate.
Check you connections and mount the plate

Spider II Mod

I never did this mod but I did stay at a Holiday Inn Express last night.

Make your cable

The cable usually only needs to be about 3 long. Use 2 of the NL4 cable mounts and wire 1+ to 1+, 1- to 1-, 2+ to 2+ and 2- to 2-
But I want to be able to use it without the cab
Use the remaining NL4 to make a dummy short. Use to small pieces of wire to short 1+ to 1- and 2+ to 2-. Put the dummy plug in when you only want the internals. Pictures
Contributed By: Pete Melton Atlanta, GA (Checkout DogHouse)