i've had this weird thing happen to me every once in a while:

when i'm starting my 1984 westfalia, the horn would blow when i turn the
key to the "on" location, i haven't turned over the engine yet, and i 
back of the key, take the key out, and sit there wondering if the engine
will blow up soon 
(soothing female voice: "Self Destruct Sequence initiated...you have 
                         15 minutes to disembark Vanagon, have a nice day"

WELL, i've finally figured it out...sometimes, when i put in the key, 
another key from the key chain will be touching the metal in between the
steering wheel and the steering column...no sound, then when i turn the
key to "on" the horn will sound...

i guess i'll have to tell the good reverend that the exorcism is off.