Wiring power Through the MTH AIU to Track or Accessories.
This section shows how your can run your power directly from the transformer or from a TIU output through an MTH AIU switch to remotely control power to track or accessories.  The AIU uses internal 10amp relays.  Since this is the maximum amperage from the MTH Z4000 transformer and other transformers you can essentially run power through and AIU switch to control or run anything on your layout including your trains as I did.

Although you do not need to shut power off to your MTH or Lionel trains that use the digital control systems like TMCC for lionel and DCS for MTH, you may still want to power off conventionally controlled engines, reduce power consumptions particularly for lighted passenger cars or eliminate interference to your control system from other types of control systems.  Also, even though MTH engines can sit on a powered track and draw very little amps, the internal DCS hour meter does run, adding hours to you total hours used when it is not even running.  For these reasons I have connected power for different blocks through the AIU switches.

Both of the Black Diamond Railway video illustrate how to do this, however, I will repeat some of the explanation here. 

The diagram below is from one of the DVDs.  The red arrow points to a small section of track for the left side of the engine house on the bottom level.  This section is isolated and the center rail is powered through one of the AIU switches.  I can use the DCS remote to apply or remove power to this section of track and the engines on them.  Note, when applying power to an MTH engine while the TIU is already powered, will cause the MTH engine to start up in conventional mode.  In this case, I simply select it with the DCS and shut it down and start it back up. 
The diagram below shows how to wire the single power wire through the normally open conncetion of the AIU.  The ground wire can be wired directly to the outside rails of the track.   Normally open means that when the TIU and AIU are first powered up, the switch contact from the "IN" to input "1" are not connected or normally open.  At the same time, the contact from "IN" to input "2" are conncected or normally closed. 
If you want the section of track to be powered on first power up, then you wire the power between "IN" and input "2".  If you do not want power on this section of track when you first power up, like I do for this engine house track sections, then you wire power between "IN" and input "1".  You will then have to program and use the DCS remove to change the position of the switch from its "normal" position on power up.  So when you activate or turn on a switch using the DCS remote, it will connect "IN" to input "1" as show below.

  My second DVD, "The Black Diamond Railway Part II" illustrates these techniques and shows you how to program the MTH DCS to control the AIU to control both accessories inputs (ACCx) such as signals and powered accessories, and also switch inputs (SWx) for controlling momentary contacts like switch machines. 

  The image below shows how to wire through the "Normally Open"  contacts for ACC6 of the AIU accessory switches.  In this image the black wire was actually a ground wire which you can also control through the switch.  You can just as easily run a powered 20v 10amp red power wire through it as well.  Also note, the Accessory switch will stay in its position until changed by the MTH DCS remote or powered off.