My empeg-through-headunit-with-speakerphone install had been working great around town. I headed from DC to Pittsburgh and back over the holiday and began having problems.
The amusing version: after about 2 hours of driving, rolling up my window all the way would cause the stereo to mute for a moment, then unmute. Then, rolling it down all the way would do the same. Then, about 20 minutes later, braking caused the same behavior. Pretty soon, it was muting on turn signals, acceleration, whatever. Finally, it just stayed on mute.
Removing the empeg (which wasn't muting, except when the speakerphone system requested it, of course) fixed the problem with the stereo. I reverted to CDs for the rest of the trip.
I suspect the problem is that both the empeg and headunit are wired to the speakerphone's (a parrot CK3000) mute line in parallel. The potential at the sense input of the empeg vs. the sense input of the headunit aren't the same, and therefore a current running from the headunit into the empeg, when installed, that causes the headunit to be close to or at the transition point it recognizes as close to "ground" than "+12". As the unit heats up, it gets pushed over the line.
I'd like recommendations on a solution. Would a couple of diodes, each between the headunit and empeg and the common connection to the mute line fix the problem? If so, can someone with experience recommend a type/specification?
Thanks again and again...