I have 1989 boat with Johnson controls with the big red plug trying to connect to 1999 50 hp motor with two 6 pin plugs and one 3 pin plug. I have the wiring diagram for the big red plug but no information on the 6 and 3 pin plugs.
I have a sacrificial harness I could use to make an adapter but not sure about the wiring.A dealer may have an adapter cable.----Or do it with a terminal board and bypass " plugin " convenience.