How to be sure it's the starter -Mercruiser 5.7

[Begester]

I have a 1989 searay 220da w/ 5.7L alpha 1. Yesterday I put the boat in the water and it wouldn't start. No click or anything...I just turn the key to start and get nothing. Took it home and have been diagnosing the issue. Batteries are both 12v, all other systems work fine. Gauges engage when I turn the ignition one click.

I went to bypass the solenoid tonight and after a bunch of Sparks, I get a winding noise coming from the starter. It is NOT indicative of trying to start the engine, but something is spinning inside the starter. Does this mean the solenoid or starter is bad? I thought that if the solenoid was bad, bypassing it would cause the starter to engage and turn the engine over.

Any insight is greatly appreciated.

 

[Bondo]

Ayuh,..... If you by-pass the starter mounted solenoid, the bendix won't engage the flywheel, so only the starter spins,.....

When you turn the key to Start,..... is there power at the tiny terminal with the yellow red wire, the inner most tiny terminal, nearest the motor,..??

 

[kenny nunez]

There is another solenoid that engages the main starter solenoid. When you tried to jump the starter you crossed the main battery post to the copper strip going into the field frame. The boost solenoid has a red wire that is always hot, a small yellow/red wire from the ignition switch and a larger yellow/red which goes to the starter solenoid. Get a test light and remove the coil wire so the engine does not start. Probe the boost solenoid terminals while some one turns the key. You may hear a “click” from the solenoid. Most times that solenoid is the problem. If you get current out of the boost solenoid then the starter has to be replaced.
One of the other posters on this site can display the wire schematic which may help.

 

[Begester]

Bondo - Just tried the terminal with the yellow red wire nearest the engine. No voltage when I set one side to this and the other side of the multimeter to the ground on the battery.

When I manually connected the terminal with the yellow red wire to the solenoid terminal with cable from the battery, full starter engagement.

Does this point to solenoid?

 

[scoflaw]

Reread post 3, Is power coming and leaving from the slave solenoid ?

 

[Begester]

Just checked the slave solenoid...12 volts across the two large terminals at the top when key is turned one click to the right. When I manually connected the two terminals together, I get full starter engagement.

Does this mean I've ruled out the slave solenoid? Thanks all for the assistance...I'm learning a lot about the system with this!

 

[Begester]

Also checked the two small terminals on the side of the slave solenoid. No volts between the two, but I'm getting 12 volts when I connect eacheof the side terminals to the hot side of the upper terminal on the slave solenoid.

Note that I get no "click" when trying to turn the ignition switch to start the engine

 

[scoflaw]

If you have 12 volts on the small y/r slave terminal when you turn your ignition key to start, and the starter cranks when you jump the 2 large terminals together, you have a bad slave.