1983 Mercruiser 898/198 Voltage Drop Cranks but No Start

[Bruce57]

A little background boat was sitting for extended period of time and getting it back up and running, fuel replaced, carb rebuilt, new batteries so time came to fire up and she tried to fire then just cranked weak spark so bit the bullet and replaced the old Thunderbolt IV with a Delco Voyager EST after some frustration with wiring and yes shift interrupt switch is ok it appears to be working correctly but once again when you turn the key she wants to fire in first second but then just cranks so out came the Voltmeter and good voltage 12.5 + across the board but once start cranking drops to 8.5 across the board meaning every hot or positive connection on the boat has same reading. I thought well it’s a new battery 1000CCA and new doesn’t mean squat so hooked up a charger and a jumper back but still get the same result I’m stumped and wondering what am I missing

 

[Bondo]

A little background boat was sitting for extended period of time and getting it back up and running, fuel replaced, carb rebuilt, new batteries so time came to fire up and she tried to fire then just cranked weak spark so bit the bullet and replaced the old Thunderbolt IV with a Delco Voyager EST after some frustration with wiring and yes shift interrupt switch is ok it appears to be working correctly but once again when you turn the key she wants to fire in first second but then just cranks so out came the Voltmeter and good voltage 12.5 + across the board but once start cranking drops to 8.5 across the board meaning every hot or positive connection on the boat has same reading. I thought well it’s a new battery 1000CCA and new doesn’t mean squat so hooked up a charger and a jumper back but still get the same result I’m stumped and wondering what am I missing

Ayuh,..... Welcome Aboard,...... Sounds like a corroded wirin' connection,....
Both the positive, 'n grounds need to be taken apart, 'n cleaned to shiny metal Clean,....
Another possibility is a cable with internal corrosion,.....
A third could be a weak starter, bad brushes, etc,....

 

[Bruce57]

Ayuh,..... Welcome Aboard,...... Sounds like a corroded wirin' connection,....
Both the positive, 'n grounds need to be taken apart, 'n cleaned to shiny metal Clean,....
Another possibility is a cable with internal corrosion,.....
A third could be a weak starter, bad brushes, etc,....

That was my next project Boat was kept inside garage out of weather connections look good and starter works fine but yeah that was my next thought