It does sound like a wiring problem. The fact that it stopped working when you put it back in the water may indicate that there is a small break inside the feed wire somewhere that when the weight of the pump pulls on it, causes it to separate, thereby stopping the pump working. Is it worth trying a new length of feed wire? Very cheap to buy from B&Q. The offer still stands if you want to send it back to us - I'll have a look at it for you.