Ok this must truly be the dumbest thing I’ve ever done. We have a brand new radar detector and it mysteriously stopped working. Turns out that the lighter adapter has a mini-blade 2 amp fuse in it. There is a easy to push button which releases it.
So next time your Valentine doesn’t work, look in your glove compartment for a fuse down at the bottom. You insert it in and give it a firm push. Oops!