What model? Most vehicles, the interior light or horn fuses are safe options, or a fused supply directly from battery. Two important considerations are (1) the total current draw of your plug in device PLUS the original circuit, the fuse needs 50% spare capacity, ie a circuit with a continuous draw of 12a would require an 18a fuse, therefore you would need to fit a 20a fuse as it is the next size up. An intermittent 12a circuit would get by with a 15a fuse, but continuous would overheat and blow after a while. (2) If you tap off an existing fuse make sure it is not a critcal one, ie don't run minor accessories, or devices that are likely to blow a fuse off your engine, charging, wiper, stop light circuits. Cig lighter type plugs are notorious for blowing fuses.
