Look in the slot behind the Steering wheel  and make sure that the copper
color ribbon ring is not coming loose.  Happened to me when the vanagon died
on the top of an off ramp -- restarted and horn started blowing at the car in
front of me --- sounded just long enuf to make it seem like an intentional
honk.  Then it proceeded to do the same thing as I drove down the road --
with each slight turn of the wheel.  Each time pissing off another driver in
front of me.  After five or so, I pulled over and inspected to find the ring
a bit off and bunched up.

Charlie.
PS if it not that, it may be possessed -- I sure thought mine was