The ignition coil on a Stihl chainsaw, more commonly referred to as the ignition module, sends a high-voltage electric current to the spark plug, igniting the fuel in the combustion chamber. When the flywheel spins fast enough along the crankshaft, the two magnets, one on the flywheel, the other on the module, align and the charge is sent up the line. The coil body also has a short-circuit wire that runs to the stop switch on the control handle. Since the ignition module uses high-voltage electricity, you should not handle or remove the ignition module without the proper tools and knowledge.
Set the Stihl chainsaw onto a bench that is fully grounded. Move the master control lever into the "STOP" position. Unscrew the four retaining bolts holding the fan's housing cover in place over the cooling system. Lift the fan housing cover off the chainsaw.
Disconnect the short-circuit wire, the thicker of the two wires, and usually at the bottom of the ignition module, from the tag on the ignition module. Wear leather work gloves and use the needle-nosed pliers to gently pull the wire free from the tag.
Loosen the two bolts holding the ignition module onto the engine and take out the bolts. Pull the ignition module forward slightly. Pull the short-circuit wire slowly from the retainer.
Push the metal baffle -- it looks like a horseshoe -- towards the fan wheel and, slowly and carefully, pull the ignition lead wire from the ignition module using the needle-nosed pliers and leather work gloves. Lift the ignition module off the chainsaw.
To replace the module, set the new ignition module into its seat on the engine. Thread the screws into their slots but don't tighten them. Insert the short-circuit wire back into the tag on the ignition module. Set the wire in place under the retainer. Set the ignition module setting gauge in between the ignition module and the flywheel magnet poles. Press the ignition module against the setting gauge and tighten the mounting screws to 3 foot-pounds (4Nm). Insert the ignition lead wire into the ignition module. Reattach the fan housing cover and tighten its four bolts with the screwdriver.
Do not take apart the ignition module. The high-voltage spark delivered by the ignition module can be lethal.