So, how does one test the sub-componants in a HID system?

The car I am currently looking at is a Volvo V70.

Neither light works.

The Bulb is fitted into a ballast that sits where the bulb would normally go in a conventional headlight.

There is a three terminal connector leading to this.

What voltages (trace) should I be getting on these three wires?

I suspect that I am going to have to replace the ballasts anyway because the contacts are partially burned away. But it would be nice to do a proper diagnostic rather than just throw parts at the car until it is fixed.