Help, engine does not start

[Runner37]

I installed a brand new Moyer marine atomic4 in my allied luders finishing last August. It ran great. This spring it acted like it wasn't getting enough voltage when I started it so I replaced the batteries. It started but acted like there was still low voltage the next time I started it. I left it for two weeks and came back. It cranked once then nothing. Batteries are fully charged. I have checked all of the wiring, cleaned all of the battery posts, installed a new solenoid, hot wired the solenoid and don't even get a click. Is it the starter? Seems unlikely. I hand cranked the engine with the plugs out, it turns just fine.

I have12.7 volts at the big post from the battteries to the batt post from the battery switch and ignition. From the st switch on the ignition to the s post on the solenoid I get 12.7 volts with the ignition turned on. I have checked the continuity of all the grounds. The ground from the solenoid is to a buss bar which is grounded to the rear of the block. I jumped it and checked it and it's good.

I'm stumped. Help! I'd rather sail than work on my engine.

[ndutton]

Please take a few more voltage tests for which you will need a helper.

1. Two tests from the large solenoid post to two different grounds while the helper is pushing the start button/keyswitch in the cockpit. The two grounds are the engine block and the battery - post.
2. Same two tests except between the solenoid output strap to the starter and the two grounds.

What I'm suspecting here is a cable or solenoid issue. With such a problem you'll read voltage at rest but it will drop significantly under load (during starting). The reason for the different grounds is to home in on which cable. I admit it's a guess but one I'd like to see confirmed or eliminated.