MTH AIU

The yellow wire is to drive the LED's in the Fastrack switch, you don't connect it to the AIU as there are no LED's to light.

Thanks John, I took the track jumper out of the switch to run it on 14v.  What will power the LED if you don't use the yellow wire?

I think the yellow wire provides power to the remote control switch LED, not the track switch LED.  I am assuming the wires you are connecting to the AIU are the wires you removed from the remote control.

Thanks Moe

Moe is correct, the yellow wire is JUST the position indicator for driving low current lamps.  You still need to provide the switch power.