My bike too had same issues recently. I also own Sprinter. I did the following too things,
If the spark plug and plug itself are in good health then remove the plug from the cable and ask electrician to cut and reshape the cable edge. This fault generally can not be caught easily.
Open the battery cover (the metal plate under the plastic side covers). Look inside the cavity, at the bottom left (near to the engine there is small grip with two wires. If you disconnect them neutral light goes off make sure it is in good health, not melted or lose.
During ride it gets hot due to losing or get lose due to vibrations, resulting in no neutral light engine shuts down.
