I think you have a short

Do you have a soldering iron and/or or a set of alligator clip wires? If not, get some of the wires (harbor freight carries them), a 12V lightbulb (NOT LED!), and a socket to fit it - any old 12v lightbulb and socket will do, as long as they have wires you can clip your alligator clips onto. Trailer lights are usually easily available, again I think HF sells cheap sidemarker lights. Then, take a blown fuse, and break off the plastic off the top around the test points. You can then either alligator clip or solder wires to the top of it, and connect them to the lightbulb. Stick it in the taillight fuse socket. This is now your short indicator - when it's lit up bright, you have a short, when it goes dim, you've fixed it. Now, you can safely turn on the indicator lights and go around the car, wiggling wires, removing bulbs, etc, and checking what makes the short go away until you find the problem. I would strongly suspect a shorted out light bulb, but the tool will help you figure out which one without spending an arm and a leg on fuses.
BTW, I think they sell tools that basically do the same thing as this, but I usually have all the stuff to make the tool lying around (and have lost the last one I made).