I had a fancy Mercury
multi cylinder 2 stroke
from probably earlier than yours. Well, my problem turned out to be the wiring
on the engine
. The rubber wiring insulation
had cracked, moisture had got into the copper core
and the actual conductor part had become powder......
It was so bad that the main positive couldnt pass enough current
to turn the starter and the exact same thing was playing out to various degrees on all the other wiring on the engine
. Of course nobody makes replacement parts
for most of the bits concerned so mine was only good as a donor source for parts
for someone elses engine.
Just unbelievable how expensive a simple 20-50hp outboard