Greetings!

Um, that sounds strange. There is an amp signal line as part of the connector. While you could use the power antenna line for the amp trigger, I would think this wouldn't work unless you had the tuner as your source.

Now, as to this suddenly happening, you might want to double check your wiring. Something is shorting, assuming that no wiring has changed or been modified recently. Check for any connections having pulled from the harness, or a splice grounding somewhere it shouldn't.

Also, how do you have your headlight sense line set up? Where are your connections leading?