I have a battery holder that came out of an old remote control car that holds 8 AA batteries in series. That equals 12V and usually has enough power to supply a two to four head fixture. I would recommend having something like that around for testing. I would personally say the white rectangles is the negative, but it sounds like a custom re-wire job so you just have to test (or take it apart and check where they connect to the circuit board). These lights are generally rated between 10 and 14v so I wouldn't make a habit of dropping down to 9v for testing.