Switched fuse or Relay location?

[Lew]

The Wife's VW Beetle came with a Solar Panel for keeping the battery up when parked for long periods of times, etc., like at an airport lot. It's about 14" x 10" overall, and the charging panel is about 8" x 9". It also has suction cups on the four corners to attach to the windshield. It plugs into any cigarette lighter. Part # is 1CO 915 687 max power 3.2 W voltage at max power 18.8 v current at max power is 170 ma. We have never used it. I did check it out by attaching my volt meter to the + and - sides of the cigarette plug. In the bright sun I got 12+ volts right away. Been thinking about taking it along in my fishing boat. Could run a 12 volt bait bucket, or keep charging the battery on anchor. That's the ticket!