VP Holden / Toyota Lexcen VXi Horn Problem

[The Other VP]

Have a 2nd hand (new to me) 1992 V6 Toyota Lexcen VXi Wagon, that suddenly started to announce it's presence to the world, with a continuous sounding of the horn at about midday, apparently after having been heated up with the Sun.

Vehicle had been driven earlier in the day, but had been parked unoccupied, for several hours before this event occurred.

Disconnected the battery to stop it, then saw the fuse / relay box above the battery, with a 15A Horn fuse, that could have been used to disable the horn easier.

Anybody out there know the possible / probable source for this unexpected, horn blowing problem ? ? ? ? ? ? ?

( Needless to say the Day Sleeper next door was not a happy camper with the racket )