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Most mower engines are negative high volts with positive ground. That means if you attempt an electrical conversion of sorts for alternative energies, the ignition current will bypass the spark plug altogether and jump UPWARDS from ground up through a grounded resistor, grounded coil L, grounded capacitor C, or tap wire to ground. You will wonder why your added circuit doesn't work. The S1R9A9M9 coils assembly used on 18HP Briggs mower engine that ran on water 2008 was in conjunction with sufficient moisture at plug tip so that, having lowered ohms, the plug fired with the added 15 amps and upper voltage added. The misfires heard during the running engine was due the unregulated smooth flow of water that at times allowed a much higher NEGATIVE voltage to form which then would jump through another path rather than the effort of the plug gap. Problems like this can be eliminated by removing the SS Magnetron- ignition coil or armature as it is called, and changing this to POSITIVE high voltage to standard negative ground. Needed- one new pre 1982 Magneto ignition coil, OEM by Briggs and Stratton not aftermarket type as they can't be used. B+S 298968 in red /white box. Also the solid state conversion module kit #394970. The flywheel spins same clockwise direction but you want induction from magnet to form PLUS + positive current. Magneto is to be mounted upside down with large rivet heads underneath. The sliding trigger module should be seen on the leading side, as with (the Negative mode). This is all contrary to normal negative operation. Heat with solder gun and separate the two ground wires with pliers and heat + solder braid removal strip. Module also needs wire slid out and away from spring clip. Put screw vertical in vice and push module tube down upon it, raising up the clip and remove wire away. Then grind down this plastic tube flat , carefully down to edge near bottom of transistor. File minimum plastic on right side of coil (small rivets up),for room for module. This is a very tight snug fit, so that the trigger coil is under flush- with metal armature flat angle. Three wires are grounded to armature metal hole with screw and nut ( secondary bare ground, Primary loosed sheathed black wire and module wire with ring terminal. The 4th wire is other end of primary - the one with baked on brown insulation. This is hooked to module wire that was removed from spring post. Use wire connector type that has dual set screws. Package of 10 can be sawed separate. The completed hand assembled SS conversion coil is then mounted with feeler gauge at each end to flywheel edge about .006" or width of a business card. Then attach in series with high voltage output - one Microwave diode 15Kv .75 amp, cathode facing spark plug. You will now have positive high voltage , verified as firing spark plug with diode, and about 2000 Volts by this method, much less than the negative sense, but doubles when under compression rather than fired in air. The Negative normal Magnetrons have this SS kit built in and covered with epoxy. It's made to work only in one direction with spinning magnet on flywheel. Now your added circuits can be tested without interference from negative Briggs coils. An ohmmeter can be used to identify opposite ends of the primary and secondary of magneto. The Stens brand trigger uses the volts generated by primary winding so as not needing the spinning magnet for turn on/off. It's easier to mount with the coil.