how do i wire up an interior accessory light?

i have an interior black light i wanna wire up. 1 positive and 1 negative wire make up the connections. it says the red wire is the positive and the black negative, but the wires aren't red and black, there clear and clear with a white stripe. a friend told me to put the positive wire in a fuse (in my case a 10amp left headlight fuse) and put the negative wire on a bolt on the body (or any other ground). question 1: is this the proper way to wire up my light? i put the clear wire in the fuse hole, stuck the fuse in it, and took the clear-stripe wire and touched it to a bolt on the body. i turned the lights on and the light didn't shine, but the light came on. i checked for the correct fuse...it's the right one. so, i did the opposite...took the other wire, put it in the fuse gap, stuck the fuse in, touched the other wire to the bolt, turned the headlights on, and still no blacklight. am i going about this in the right way? what the f- am i doin' wrong?