Yeah, I have to admit, sheepishly, that I didn't RTFM regarding the default setting of the sense line (ignore). It's now set to mute on 0 volts (grounded), but I haven't wired the line back into the harness yet.

I'm curious about one thing. The other articles indicated that the pull-up resistor is now integrated into the MkIIa model, which both of my empegs are. So, no resistor should be needed.

Would it be correct to say that a resistor is integrated into the MkIIa model and acts as a pull-up resistor when sense is set to 0V, and as a pull-down resistor when sense is set to 12V?

If so, is the resistor completely out of the circut when the sense is disabled or does it default to one of the two positions? The answer to that might explain why it interfered with the headunit/speakerphone when disabled: I seem to recall something about odd behavior with open-collectors that don't have a pull-up/down resistor. Alternately, perhaps the default resistor "position" for the mute-disabled empeg was incorrect for the sense-0-volt circuit.

-brendan