Gearbox problem?

[HelpMe!]

I started to notice problems with my automatic mondeo recently. The 'o/d off' was sometimes flashing on my dashboard and when this happened, the car would over rev before changing gears, the changes would be juddery and sometimes the car stalled when I came to stop at a junction. 

 

So a little searching online lead me to believe that there is a gearbox problem if 'o/d off' is flashing. Today I removed the air filter and battery so that I could see the gearbox to look for anything obvious. I found a hose which I think is connected to the gearbox, but then the other end was hanging loose. It looks like it should be pushed on somewhere, but I just can't seem to find where!

[HelpMe!]

Just been searching and think it's actually a breather pipe, so not the cause of my problem. 

Any ideas what could cause the overdrive light to flash and the problems I described?

[HelpMe!]

There is a round electrical connection on top of the gearbox. I took that off and it had quite a bit of moisture in there, but no corrosion. Tried drying it out as best I could and reconnnected everything. Took it for a drive and got about half a mile before the o/d started flashing again so I went straight back home. The engine management light has been on for a while, but my code reader isn't showing me anything when I plug it in.