I need help. I changed out the zinc on my rudder shaft a couple of weeks ago and found it to be severely corroded, while the zinc on my prop shaft was hardly corroded at all. My boat is bonded. I checked for stray current where the bonding wire is attached to the rudder quadrant and found about a third of a volt dc passing through at thirty three milliamps. Positive was on the wire side, negative on the quadrant. I looked for a fault onboard. I methodically disconnected various electrical inputs, but the voltage remained. I finally disconnected all of my batteries at the positive battery terminals and unplugged my shore power cable at the dock, but the voltage still registered the same one-third of a volt. I don't get why with everything disconnected, the voltage is still there. Any ideas?