Ok...ran the heater for a couple of hours now, the cab is toasty(with battery hatch open).
Plugged the battery tender in, and we've got an intermittent yellow light. It's not "flashing", its more of a pulse. Here's a youtube video of what it is doing:
http://youtu.be/jkBoeBtsBGs
My other battery tenders stay steady yellow when charging(and I suspect this one should too...instructions were missing from the box). I checked all of the connections, everything is correct and making good contact. I connected it to the same terminals the trucks main power cables are connected to.