Hi dbun,
Went through some pain getting the antenna working on my VT, but is actually quite simple. Here is the guts of it.
1. If you use the wiring harness as most people suggest, then it will connect the blue wire from the HU to the Yellow/Red in the wiring harness. This tells the antenna control unit that the radio is on. It doesn't supply power to the motor, this comes directly from the battery.
2. If you had the antenna up when you took out the old HU then it should go back up to that spot when you hook up the new HU.
3. If you had the antenna down when you replaced the unit (like I did) then the antenna stays down. Read on to find out how to fix it.
There are 2 wires in the harness to control antenna UP (Light Blue) and DOWN (White). To control the antenna height, connect EARTH to either the UP or DOWN wire. Not 12V. Once you have it in the spot you like, simply leave them unconnected in the plug and the antenna will return to that spot when the HU is on and go down when the HU is off.
If you want to control it, you will need to put a 3 way rocker switch somewhere to switch EARTH to either wire.
You should be able to find wire colours and a schematic here on the forum. Both helped me heaps but feel free to email if you have any questions.
BTW I ran a separate earth for the unit.
Muttley