In a previous question regarding my dashboard lights not working I found that the "tail" fuse would burn out immediately upon turning on the headlights.
This is after someone did repairs to the horn, and pulled out bunch of extra wiring that had been put in to support an after market horn.
Are there any good guides on the net which could help me with how to track down a short circuit like this?
As Zaid said, start with crasic's excellent answer in: How do you test analogue electrical circuits? .
For your situation specifically, I would introduce a small voltage between the fuse holder of the fuse that is blowing, and ground. Use a continuity noise generator or a light bulb so you can hear or see your progress.
Then, get into that bundle of wires near the custom horn setup and selectively disconnect things until the current flow goes away. What you are looking for is a place where the current is reaching ground (another wire or vehicle chassis).
As for "good guides on the net", the purpose of this site is to build that good guide, not send people willy-nilly over the Internet.
