Re: 1968 johnson 55hp won't start
#1 make sure that it is in neutral, and that it knows it's in neutral. there are a lot of small wires in that wire harness, and being 40+ years old it could very easily have a break/cut/worn spot that could affecting it. When you said it makes a thud in the lower unit when you connect it to a battery, it makes me think that it may be in gear.....just a thought. My first outboard was a 1969 Evinrude 55 hp electric shift, and one of the first things I did was a lot of wiring and re-wiring...but it was worth it when I knew it would do what I wanted it to, when I wanted it to.