the green wire issue....
It's MotherMoto that recommends the green wire/red wire co-connection for all their products configured thusly. The radio drawer and the control head use a form of binary communication to "talk" to each other. Without getting onto a laborious and technical dissertation on the pros and cons of this arrangement on an obsolete but great radio series, there's simple way to look at it. If there's much more than a few millivolts potential difference in what the radio sees between the voltages on these two wires, there is the strong possibility that noise and voltage spikes riding the potential difference can be sufficient to be interpreted as control signals and cause the radio to do some really strange antics. It's just best to save time and follow the recommendation and not question the lack of sufficient filtering to combat this or a different power source arrangement that would be less susceptible to the interference. The radio is, after all, no longer manufactured and is "out of sight, out of mind" as far as Mom is concerned.
Me? I've had durn few to give a problem over the years, but there were a couple "installed by others" that had caused the installation people and the techs to pull their hair out simply because they had failed to read the installation instructions. The whole issue with these radios isn't really that you've got the green wire connected to a source other than the battery, it's that the radio doesn't see any potential voltage difference between the two wires and the ground is common to both voltage sources. The worst I ever saw was the one on an ambulance that had the red wire connected to the right battery and the green wire connected to the accessory control panel which was tied to the left battery. Add the battery isolator into the mix along with the bum ground connection between the box and the cab and there's no way to describe the numerous intermittent antics that were created by the varying voltages the radio was seeing. Grab 'er, Newt! She's gonna buck!