+1 on above comments. On cleaning up the connections, disconnect them and clean the part where the current flows. What they look like on the surface doesn't affect performance. Other thing is the crimp on cable connections could also be corroded and probably unable to see it.
However your comment is confusing. 13v at the solenoids when? If you are pushing current through your wiring and getting no results at the load end (starter spinning up, pump not pumping, then part of your battery voltage is across the failed part...aka dirty connection if that's the cause. The dirty connection causes a resistance in the circuit and pushing current through it will develop a voltage which is deducted from the batteries available output.
Example is you measure from the engine block to the battery cable attached to the pos terminal and get 13v with your switch to the starter or tilt/trim engaged. You go to the starter motor and read 10v at the voltage input terminal to engine block ground. Somewhere along the line from one to the other you are dropping 3 volts and that is where your bad connection exists. Could be the contacts of the solenoid or could be the wiring into or out of the solenoid.
You didn't say where you put your ground lead. If it was on the negative terminal of the battery then the ground wire between the battery and the engine block is your smoking gun. If it was on the engine block then something is dreadfully wrong as things just don't add up. However, with all solenoids showing the same thing and assuming again that you take your readings with the switches closed, then I'll go for the ground connection as stated.
On lead battery terminals, remove the terminal and using a wire brush specifically made for the purpose, shine up the battery post and the inside of the wiring connector. Auto parts stores carry this brush in the battery accessory dept.
That's the way it looks from here.
Mark
