4.3 Mercruiser turns over with ignition intermittently

Here is my situation, 2000 4.3 Mercruiser will not turn over every time the key is turned on. I can turn the key to ignition and only get a loud click from the solenoid at times. I will turn the key back and forth a few times and it will sometimes engage the starter motor and it starts just fine. I have replaced the Starter Solenoid, the Slave Solenoid and rebuilt the Starter but still have the same problem. I can here the starter solenoid click every time the key is turned but the starter only turns over it seems when it feels like it.
Anyone have any suggestions or comments.

Thanks in advance.
Gary

clean/replace the neg battery cable connection at the block

Thanks Bt Doctur, I checked all my battery connections, cables and cable connections and used a multimeter to test the cables. Still doing the same thing. Pulled the starter motor and solenoid and bench tested them with jumper cables and a test switch to activate the solenoid everything worked fine.
Is there something in the ignition system between the slave solenoid and the starter solenoid that I am missing that may be causing my grief.

On another note, i tried replacing my exhaust bellows between the transom and outdrive unit. Does anyone have a trick for pulling the bellows far enough to attach it to both ports without removing the outdrive unit.

Again, Thanks in advance.

don't think you can attach the bellows without pulling the drive,check your intake hose because you can do that while you are there.I used a pair of modified tongs to pull the bellows aft through the exaust cavity,theres also a special tool designed for it.

As Bt Doctor mentioned.....clean or replace the negative cable. Actually, I would recommend cleaning all engine area connections, wire brush, sandpaper, contact cleaner, compressed air, the apply dielectric grease. This simple and basically free maintenance can work wonders...seen it fix many a boat. Good luck!

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Maybe the next time it doesn't crank right away, pull the spark plugs and see if any of them are wet with water.

A quote from your original post. "I can turn the key to ignition and only get a loud click from the solenoid".

This is a clue.