I am having a huge voltage drop at my starter!!! please help

I was fishing and went to crank my boat up to head in and it turned over really slow. It seemed to me like the battery was almost dead so I swapped with my trolling motor battery and had the same result. When I got home I tested the voltage at the starter and it was dropping from 12.6 to around 8 volts. I replaced the starter and am having the exact same issues. I have load tested the batteries and both are good. What else should I do?

Re: I am having a huge voltage drop at my starter!!! please help

My bet is that there is some corrosion inter main battery wires. Disconnect the power wires at the battery and connect jumps cables to the starter + post, and engine ground as well as the battery. Then give it a whirl. If it fixes it then you need new wires.

Re: I am having a huge voltage drop at my starter!!! please help

It could also be a bad connection to engine ground, bad connection to the hot post on the solenoid (from time to time it's a good idea to clean all those connections), or a bad solenoid.

In my own words here's the test that is spelled out in OMC factory service manuals.

Measure the voltage between the + battery terminal and the hot post on the solenoid while someone momentarily cranks the starter, it should be less than about 0.3 volts.

Next measure the voltage across the solenoid terminals while the starter is being cranked, likewise it should be less than around 0.3 volts.

Measure the voltage between the + side of the starter and the output side of the solenoid while the starter is being cranked, again it should be less than about 0.3 volts.

Finally measure the voltage between the - battery terminal and a good engine ground while the starter is being cranked, it should be less than about 0.3 volts.

If any of those values is high then you've found a problem.