Pretty sure the left contact is power and the right ground.
If you block off the right contact, the one-seg tuner still works (guess being because there's still ground built in to the usb)
If you block off the left contact, the tuner doesn't work.
UPDATE:
Well, I did a simple test of reception by covering the tuner pcb with electrical tape and just sticking it in the umd drive area. reception gets totally cut off... so some kind of external antenna is required which is what I thought, but hoped wouldn't be true.
There's an extension cable that was just released in Japan that goes from the one seg tuner to the wall cable jack, using your house's antenna for reception. Don't really see the purpose in this, but whatever... my theory is that the cable itself should act as an antenna and the cable connector can just be cut off.
In any case, this project won't be anywhere near final until some slim full cases are produced. I don't wanna cut up my red slim.