4.3 Mercruiser Vortex

[My3girls]

Replaced both batterys (950 cca) tapped the key got good crank, put the muffs on and got a small crank then nothing. Replaced starter, solenoid, checking plugs and wires tomorrow, all cables to batteries are clean and tight. Any suggestions?

 

[AllDodge]

Use a voltmeter and trace power
12V on Bat, then check starter, then check 50 amp breaker, then check slave solenoid.
Go behind the helm with the key switch, check red/purple wire, turn key ON and is there 12V on Purple wire?
When key is turned to start is there 12V on the Yellow/red wire?
Let us know what you find

 

[makomark]

I'd check the engine side of the ground cable...