Basicly speaking a single stator coil is one long wire. The best way to check it is with an ohm meter,using your manual. the idea is too check both ends of that wire for resistance, the resistance values pretty much tells you that the one piece of wire is one piece of wire in good shape. if resistance is too low that means there is a break in the insulation of the wire and it is short circuiting to itself. if the resistence is too high that mean there is a break in the copper of the wire. also check for resitance from one of the ends to ground if the resistance is infinite you know the wire isnt shorting to ground if there is any conductivity between the wire and ground it is no good.
Your manual should be able to tell you what color wires should have what resistance. the idea of using an external power and test light is both good and bad. the idea is good for checking continuity but when I tried rewiring my lighting coil there was over 80ft of 22 gauge wire and depending on what you used for a light could easily smoke the wire. Also a lot of stator coils are grounded to the stator plate, In the case of my Yamaha I have 2 ignition coils 1 trigger coil and the stock lighting coil was all grounded meaning one end of each stator wire is pretty much hooked up to all the other one ends of the other coils. Doing what the manual states letter for letter with ohm resistence cannot be beat