One of the problems of all those new gadgets in our cars is that they require power, and one of my pet peeves is how unreliable those classic 12V outlets can behave. Maybe because I drive those old beat-up cars, sue me.
So I wanted a permanent connection.
What I had was; a 12V to 5V USB converter, a blank switch mount plate out of my car, and some wire and connectors. A bit heat glue and shrink-tube was added later to hold everything together.
First you have to smash the old adapter housing so you have the bare electronics. Get rid of the springs that connect to the 12V outlet too.
Cut a hole in the blank plate so that the USB connector-flanges prevent that the electronics be pushed behind the now-not-so-blank plate when you connect your gizmos.
Connect a cable to the positive and the ground points of the electronics board. I had some el-cheapo loudspeaker wire laying around that even had a marking on one of the leads to indicate the positive. Sweet.
Finish it off with some shrink tub isolation and a dab of heat (or other) glue. Just to make it a bit sturdy.
Find a connection point for +12V and Ground in your car. I just got rid of the build in clock because it was about as reliable in time keeping as a pre-Harrison grand clock. But the connector gave me the options of a permanent or a switched connection. I went for the switched one.
Snapped the plat into its slot, connected my gizmo, and done!