1988 90hp 3 Cylinder Mercury - lost spark in 2 cylinders

[MattinTally]

I started my '88 90hp 3 Cyl motor up on garden hose (serial B250374).... fire up on third try, worked great, idled fine, great pee stream... Ran for about four minutes at low idle and I shut it off and headed to the ramp, launched, motor started and ran for about a minute. Then motor stumbled abruptly and died. Turned key again and it just spun and spun, but wouldn't fire off. It just died and it didn't sound like I was getting spark. Checked routine stuff - fuel bulb, air vent on tank, opened drain on carb and plenty of fuel came out, used manual value on enricher, etc. Batteries were charged last weekend and haven't been used since, so they should be fully charged. After much tinkering, just went home. @ home, pulled all 3 plugs. It looks like i've lost spark on the top 2 plugs. Couldn't "see" spark (I've got the flat type plugs that don't have the prong) and it was a sunny day in FL. I finally just held each plug one-by-one while friend turned the key. Could feel current on only the bottom plug. Nothing on top two. I checked for loose connections and only found one -- the ground for the Trim/Tilt solenoids, which I tightened. Some minor corrossion on the coil leads, but very minor.

I've got the repair manual and read it. Unfortunately, I'm a visual learner and the book doesn't have images showing HOW to test the ignition switch (power pack), coils, trigger and stator. It tells you WHAT to test, and the acceptable readings, but doesn't tell you how to test... at least not for us visual-folks.

I'm mechanical and have worked on this engine and others before..... Have voltmeter and plenty of tools.... Just need some guidance, or better yet, a link to a YouTube video showing me HOW to perform the tests mentioned in the manual.