The 6 volt LED light strip is 100% weatherproof so you can install it under the engine grill, on the license plate frame, in the rear window or wherever you think it looks best. Rain or wetness is no issue. If you use the adhesive strip, please make sure to carefully clean the mounting surface before installing the LED strip.
If you install it in the rear window, use a bracket (thin aluminum 90degree or the like) and slide it under the window seal. Then run the wires under the window seal to conceal them.
To power your LED light strip, disconnect the battery, then run the black/blue wire (-) to a reliable ground nearby. If the 356 has a brake/tail light function in one bulb, run the red wire to the brake light wire and splice it in. If the 356 has a turn signal and brake light ‘in one’ you can either use one of the brake lights as a source (but your 3rd brake light will then blink when you use that particular turn signal) or you run a single power wire through the tunnel or under the mat to the brake light switch on the brake master cylinder for proper operation. Please do NOT use the 6volt LED strip in vehicles with a 12volt electrical system.
Example photo shows the brake light strip in a 356A single grill.