I have a 2000 sportster 883. I can't get any of the lights to turn on, the horn won't work, and the starter doesn't kick over. When I disconnect the positive terminal of the horn and run a jumper from the battery to the horn, it sounds off nice and loud so I think my ground is good and I have a fully charged battery. Testing for voltage and continuity confirms this. All the fuses are good and I have continuity across the main breaker.

I thought it might be a problem with the ignition switch, but I stuck pins through the red and red/black wires and tested for continuity. The switch contacts seem to be good. Putting a jumper between the pins didn't help either.

I pulled all the fuses out and tried powering one circuit at a time in an effort to trace any shorts or get some kind of hint as to where the problem is. Unfortunately, I saw no distinguishable difference.

There is a mysterious black box under the seat. It is filled with some kind of foamy epoxy and has two pigtails with AMP connectors at the ends. It isn't bolted down to anything. I don't have any idea what it should do or how to test it. If anyone knows what this is, could it be causing my problem? How do I check it?

The only other suspicion I have is that it seems like the ignition switch is making/breaking a ground connection whereas my manual shows that it is supposed to be switching the +12v leg. I get a resistance of around 7 to 500 Kohm when I test it with a volt meter, so I don't know if I'm picking up a ground through the lights, horn, etc or if there really is a short. I could be completely confused and measuring between the wrong points too. I intend to investigate this more tomorrow since I am out of daylight for today.

Any ideas on solving this problem? This is my first time working on this bike, so I don't know what connections are prone to trouble, where to find them, and so forth.