I noticed while running my LGB Forney today that there is a switch inside the cab. It has three or four postions it can be put in. It also has a plug in the back of tender. Is this Forney already wired for battery? Im assuming all i need to do is plug in my battery car and hit the switch in the cab for it to run. Im I correct or do I need to do something else?
Yes you can run a battery from that plug–
However, you MUST remove the sliders and brushes from the motor block.
Select Lights, motor and smoke from the switch and run it.
What I have done is replaced the LGB little square plug with a standard red/black female battery plug.
You can plug your control car in and be off down the track.
I have done this to all my smaller LGB locos, Forney, Porter, etc, and use just one control/battery car.
Thanks John. I assume by switching the switch to battery does not cut off the wires that go from track power to the motor?
Shawn,
If I’m correct the plug is for lighting trailing passenger cars–it’s a straight connection to the track.
So plugging the battery car into it would feed power not only to it, but backwards through the power pickups and into the track.
Or at least that’s how it is on LGB 2-6-0s 
Shawn and Robbie.
Yes it will feed directly to the track regardless of the switch position.
Remove the sliders, brushes and even the buss that connects the brushes together.
Don’t remove anything else.
Check with an ohm meter (continuity setting) wheel to wheel on one side and then the other side. You should not get a reading or a beep when these things are removed.