Hoist

Hey guys --
I just installed a new extra dome light in the back of my ride. I have 2 12v10w bulbs, which are powered and grounded directly from the battery. Inline, about 18 inches from the battery is a 3A fuse, and down the line there is a switch inside the cabin. The switch is a cheapo Kragen one, not marked, but only has two slots (for + and - I assume). When I finally got it working, The light is great just chilling, but when I flip the switch to off, it shorts out the fuse, every time. I went through 5 3A fuses, trying things such as reversing the polarity on the switch and such. I even tried a 10A fuse, still shorted out! I don't know what the problem would be? Why would it be fine when it is on, and short out when switched to the off position? Please help, I dont know where to look next. Thanks
rob