Yeah, I was surprised at 1.7V too. Perhaps that's worse case, as your experience shows otherwise.

Thanks for the advice on the relay coil issue. All of my relays are diode-less. In this case of this kit, the speakerphone mute line grounds on active, so I'll be energizing the coil by connecting the coil's ground connection, essentially.

When mute is de-asserted, then the ground will be cut. Well, that is, I assume the speakerphone just N/Cs the connection...would it do something else?

I also assume the coil will be trying to discharge it's stored EMF back into the 12V system (ignition wire). Not sure if that's bad or not. Perhaps it'll take slightly longer to turn the amp off than expected after the mute is no longer asserted and the stereo is off?

used the word "assume" too much, I think...
-brendan

PS - both the battery and ignition lines are fused, just in case you were worried.