I'm the idiot.

The cable has no electronics in it, just straight connections. However, it does work (sometimes). After fussing with it for about 2 weeks now I've decided to send it back and try something else. This cable is way too flaky for me, and I tend to agree with your post about having something with regulating circuitry. Definitely something more robust than this. Oh, and BTW the one I have is the ISO connector from ODB-2.com / Alex Peper.