Force had a lot of issues with the field windings under the flywheel so they built a new style stator that was supposed to resolve those issues, but honestly it DID NOT fix the problem. Your problem is due to a bad rectifier, the older 2 stroke outboard engines used a rectifier that changed alternating current from the stator into pulsating D C current by utilizing electrolytic capacitors , these create a ONE WAY door for the electricity
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The field windings for the charging system are very close to the windings for the ignition up under the flywheel. When you turn off your engine it continues to spin for a few seconds, If your rectifier goes bad it allows 12 volts from the battery to travel up to the field windings and that creates a bastard field, this overwhelms the ignition windings and in a flash it burns out your brain for your ignition. So what happened was your rectifier went bad and burned out your ignition brain. What I did in the past was to install a new rectifier and brain plus wire in a relay switch in the red positive wire of the rectifier to the battery that opened when the ignition was turned off and closed when the engine was running so the path to the positive side of the battery between the stator and the battery was eliminated when the engine was turned off. It worked great. However I later tried removing the old style rectifier and replaced it with a jet ski voltage regulator that not only changed the current to dc but regulated it to keep it from surpassing 14 volts and it discharges any excess current to prolong the life of your battery and prevent overcharging, A stator will put out 17 volts depending on the R P M. a regular rectifier will send all the current directly to your battery.
On a voltage regulator you will see the same wiring as your rectifier 3 field windings usually yellow wires a ground usually black or just the housing of the rectifier is ground and a red positive wire that goes directly to your battery, so doing a changeover is fairly simple I later did this to all my older outboard engines as well.
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In any event you will need to deal with the problem of a bad rectifier and replace the brain, check with NAPA auto parts have them look in the SMALL engine parts catalog because those people were selling all the electrical components for the old force engines back when I worked on them, perhaps they have some leftover. You will also need to replace your makeshift wiring and install a proper marine ignition switch for safety.
If you just replace the brain it will run once and then die as soon as you turn off the engine so don't do it. By the way a voltage regulator like the one in my picture can be purchased for about 20 dollars on line NEW. This info applies to the 90 hp also.
