Hi, we had the same problem with a MY09 Leopard. Everything was fine one race and the next it would not start off the key. The motor went back for a rebuild and the brushes were replaced at the same time. The motor started off the key on the Dyno but once it got back in the kart it would not turn over on the key. Nothing. No noise like the battery was dead. Because we were racing and busy with life we ran it off an external starter for a few races one of which we dnf’ed after getting spun and we could not restart.
I found a wiring diagram of the Italian motors site which was very crude. It basically showed what was plugged into the loom and where the grounds are. It did not show color of wires etc which would have been great. I worked with a multimeter and checked every wire. Finally I tried an old car trick and turned the key to the start position and tapped the starter with a small hammer. Success! It starts!
You would think that with as many leopards out there there would be some kind of simple if/then diagnostic reference and a color coded wiring diagram so we can figure out what parts to eliminate when they don’t start as opposed to having to randomly buy expensive parts in a process of elimination.
Not saying this is the cure for anyone else’s problem but it’s worth a try if you know your brushes are good, your battery is charged up, your grounds are connected and right before you sell everything to participate in a cheaper sport like polo.