Boating How-To’s - Starter Problem

I have twin Yamaha 150's four strokes, and a problem with the starter system in the starboard engine. Solenoid clicks when key is turned, but nothing else. Charged both batteries, cleaned battery posts and terminals and tightened the wing nuts with a wrench. Still the same problem. Swapped the starter motors and solenoids between engines. No change in the starboard engine. Removed the spark plugs and was able to rotate engine by hand. Voltage test shows 12+volts at starter until key is turned, then it drops below 6 volts. Current is going somewhere, but I can't figure out where. I tried using a jumper battery and cables directly on to the starter, (positive to positive and ground to engine block) and nothing happened, not even a click (not sure what I'm missing there.)

I took the double key switches out of the console. Lot's of corrosion on the metal frame (and lots of wires for two switches!!!). The starboard switch alarm doesn't sound when the key is on with the engine not running (the port engine switch does alarm when key is turned on). The gauges come on when the starboard key is turned on. I don't know how to test the switch (the wires are confusing and not easily accessible), but I don't see any obvious problems and I jiggled the wires to see if connections were loose.

I read in my Seloc manual (I don't like Seloc) that the 150's have a magnetic switch mounted on the starter (I see it). Not sure if this is also the solenoid, and wondering if there is also a solenoid relay somewhere that I'm missing?

Any other thoughts?

Thank you.

Sounds like you have a bad starter. This happens when you have a high spot on the armature. Sometimes if you bang on the starter lightly with a hammer while someone turns the key it will "free up".

Problem solved.
After having gone through every circuit on Friday, Saturday morning rolls around and I'm looking at the engine (and cursing the boating industry). My eyes are fixed on the ground terminal on the engine block as I'm thinking about everything I've done so far. Looks nice and clean. But wait- I had never removed it. So, I say a little prayer, and take it off. Voila, there is a thin layer of oxidation on the terminal. A quick scrape with a knife, tighten it up, and problem solved.
Moral is "don't trust your eyes". Or, start with one circuit and work it back, removing/cleaning every connection.