I know this is a old post but my Mk3 has just been in to a garage 7 times with this fault and after much verbal exercise we finally got a Ford Technician to come out to look at it. Turns out it was the indicator stalk. Defect started with the left indicator coming on of its own accord and then the right started a while later. Could often come to the car in the morning and find the side light on and when key was turned in ignition, the indicator would start even though the stalk was in the neutral position.