.... or you could splice into the wires feeding the Power socket in the Glove box -
They are easily accessible after removing the 2 screws holding the Glove box in place
( one outside and one inside ) and removng the glove box
( which is also held in at the front edge by two pegs pushed into rubber grommets,
so after removing the screws, pull the glove box up and backwards to disengage them ).
That power supply is live only when the Ignition is On,
so you're Garmin would Power Up and Down with the Ignition

