With my current setup, I've got the external amp trigger by the remote amp output of the headunit. As my speakerphone is wired between the output of the headunit and inputs to the amp, I have to have the headunit on in order for the speakerphone to generate audio.

I'd like to wire the amp to trigger on either the remote-amp output of the headunit *or* the mute line of the speakerphone unit.

First off: does the remote-amp line from a headunit or empeg trigger by providing +12V or by grounding? I presume +12V, similar to the "ignition" wire into a headunit. If so, it gets complicated.

The speakerphone itself triggers mute by asserting ground (or 0V) on the mute sense. So, I figure I need to get funky with some relays in order to have either line do the work.

Recommendations? This is what I have so far:

I figure at a minimum: 2 bosch relays, one wired "normally" on the remote line (+=remote, -=ground), one wired "reverse" on the mute line (+ side ignition, - side mute), with the output side of both wired +=ignition,-=remote-amp-sense and in parallel.

I don't know how many of these paths would also require a current limiting resistor and if so, what specification. For example, would I need to put a resistor in the output path, or do amps typically have a high resistance/impedance on their remote-amp-sense input? Would I need to put a resistor on any of the input paths as well?

running out of room behind the dash...
-brendan