As above - use the spare connector under the clocks. It is on the side light circuit which is protected by a 10A fuse, which is a higher rating than your satnav will need for protection against shorts. Make sure you run a separate in-line fuse of a rating fractionally above the peak current draw of your devise to protect it effectively (I use 3A) and be wary that, although live with the ignition on, it is also live when the key removed in the P position (parking lights).

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