Arnold,
Youmight try this. Connect the Z500 to aux power. Connect the Z4000 handles to the variable channels. If the red light on the TIU is on then it is powered up. On my layout I then go to the TR button on the handheld. The 2 variable tracks should then be displayed. Click on one and then turn the thumbwheel upward to turn on the power to the track. Repeat for the other channel. Sounds like you are getting power to the TIU but not the track.
Ed