2001 Cadillac Seville headlight problem

I have a 2001 Seville STS with factory HID headlamps. Over the weekend, it blew a fuse for the drivers side HID lamp. I replaced the fuse and the HID lamp lit up for about 3 seconds and then popped the fuse again. I pulled the lamp assembly out and looked at the wiring to see if I could find a pinched wire or maybe a wire that had rubbed thru its insulation and was arcing to ground but found nothing. I put it all back together and tried a new fuse, it lit up and lasted about 8 seconds and then popped the fuse again. Any ideas on how to diagnose the HID circuitry? These parts are very expensive to just try and replace ballasts, igniter, etc......Please help if you can.