Defender wiper problems

Hi folks, I have a '99 Defender TD5 and the wipers seem to have a mind of there own! - ie on intermittent setting they continue to go constant for a while then a while at intermittent then maybe constant again and even when I put the stalk up one notch to the off position they will go another 5 or 6 times or more before stopping. I have changed the relay down in the centre console in front of gear levers, the wiper motor itself and now even the wiper stalk but to no avail. Any ideas would be greatly appreciated.