The flicker when going over bumps leads me to believe that there is a bad connection at the connector. Are 100% sure that the headlight is fully seated and locked?
If the continuity is good through the headlight and good power on the car side, my first line of attack would be the connection.
I would replace the connector on the car side and check the pins on the headlight, but that would be a lot of work if you are not experienced at soldering since the new connector would need to be spliced in after the old is cut out.
The female sockets on the car side connector can get sprung enough that the connection is lost, but would still be readable with a multi-meter probe.
You can probably get a used connector from member itsnotanova on the classified forum. I've bought some from him before.
http://986forum.com/forums/boxster-parts-sale-wanted/52469-parting-out-whole-lot-boxsters.html
You might try the ignition switch before going that route since you already ordered one, but since it's only one headlight, I really doubt that it's the problem.