Small Engines (Lawn Mowers, etc.): Coil, fc540v, john deer, spark plug

Question
 I HAVE A FC540V-AS00 MOTOR, IT IS IN A JOHN DEER 180.THE PROBLEM IS I HAVE NO SPARK,THIS COIL HAS SINGLE WIRE WHITE WIRE GOING TO IT,THERE IS NO POWER SUPPLIED TO THIS WIRE FROM THE TRACTOR. I JUST GOT THIS PROJECT, AND JUST STARTING TO CHECK IT OUT, ANY HELP WOULD BE GREATLY APPRECIATED.

Answer
The single wire is the circuit that shuts the engine off when the key is turned. That wire never has power supplied to it from the mower. When the key is turned off the mower grounds that wire out to a ground to shut the engine off by redirecting the spark to ground, and not the spark plug.........Tom