There are a number of Magnadyne threads in the forum- with suggestions on how to do various things (e.g. Magnadyne M4-LCD questions
). To turn the radio off while having GPS instructions, as I remember, go to the home screen and select something you are not using (Disc? Aux?). Volume then controls GPS directions. Note that the Magnadyne (unless they have changed something since my unit) switches to "night/dim" mode when you start the Solera - the Solera uses the headlights as daytime running lights; the radio senses the headlights are "on", thinks it is night, and dims the screen. There is an icon - top left of the home or radio screen, as I remember - that switches it back to "day/bright" mode. (It is still dim relative to, say, a Garmin GPS screen - but better.) I also have found that setting the map screen on the GPS to "night color" mode - somewhere in the GPS setup screens - helps visibility of the map screen in daylight. Many of us have had to do firmware updates to avoid system resets of the Magnadyne - see the other threads if you have this issue.
Another key thing to know about the Magnadyne is the paperclip activated reset button on the front panel lower left. When all else fails...
The Magnadyne isn't great, but is workable if you learn its peculiarities. I currently use a Garmin (beanbag mount in the well above the radio) plus the Magnadyne. After adding ground loop isolators between the Magnadyne and the TV, and adjusting the sound (more treble, less bass than default) we find it acceptable as a sound system; much prefer the Garmin as GPS (though the Magnadyne GPS is working).