I start my wifes van last night and the alarm goes off. The vehicle is started and the horn/lights are flashing on/off.

I pulled the fuse for the horn and drive the van home with the lights still flashing. Everything else is working OK at this time, but alarm will not shut off.

When I get home I pull the battery cable and leave it off for about 10 minutes. I replaced the fuse I pulled and the battery cable. All is OK now, seems to have reset.

What can cause this? I have never heard of this happening before. The ignition key should have disabled alarm once it was started.