It sounds as if you have a short to earth. The easiest way to find it without a meter is to put a bulb in series with the battery and fuse. With the short the bulb will light. Move the wiring until the light goes out this will give you an idea as to where the short is. If you have a bulb holder with two wires this will make life easier. I used to do this when I was an AA patrolman to find shorts on cars.
