Horn sounding after rain

Hi all I have an annoying problem with my 04 td5 90. After a good rain session the horn will try to sound, not a proper horn blast but little blasts but last night rain caught me unaware and it went off full blast. The only way to stop it is to pull the 15 amp fuse from underneath the drivers seat. The green alarm box appears to be dry but just to make sure I'll put duct tape around it today. It happen once when in the middle of nowhere and had the time to investigate it while it was kicking off. the small alarm horn was trying to sound so I unplugged it but the main horn was sounding to. I did not know the alarm ecu would operate both horns, that if it does. I am at a loss now as to where else to look. I have searched this and I have found similar problems but no one seems to put up the solution to their problem. Can you guys help , marty