OK, I took a look at the head unit connections (it's still opened as I type this) and - whaddaya know - everything's still connected. The tuner module's red light is on, the antenna is plugged in snugly, everything looks good. About the only thing I didn't connect is the "Power Antenna" lead (I don't have a power antenna - that is, the motorized kind). The Antenna Remote, it turns out, is connected as well - presumably that's how the red light is kicking in (otherwise it would be hooked up slightly differently and the amp remote would be doing this, right?).

Not sure what else I can possibly plug in here!

So what else ... according to the FAQ I should check my tuner extension to make sure it's wired straight through (1-to-1, 2-to-2, etc.). If it's miswired I can fix it myself, get a new one or do away with the extension altogether. (I suppose using the amp remote is fine? Any good reasons why I wouldn't want to do that?)

Q: Are the antenna remote and antenna signal amp wires in the FAQ referring to the same thing? I believe it is (and it's hooked up).

At any rate, this will definitely be a priority to fix, as we definitely use the radio. Insert fun here ...