Quote Originally Posted by Mike Wilde View Post
I believe the input voltage for a CT1/2 head is about 450V. There is a third contact wire that I think is used to quench the flash capacitor dump in the pack after enough light is sensed by the head.
If you are referring to the wires actually at the flash tube, the third wire is the trigger which connects to the trigger transformer.

The transformer gives a very short pulse of very high voltage which ionises the Xenon gas in the tube and starts it conducting.

Unless stopped, the tube will continue conducting until the high voltage capacitor is discharged. A pair of thyristors is used by the light sensing circuit to stop the tube from conducting once enough light is received.