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Re: Voltage on Pedestal
This is a tough question for several reasons. Electrics are PFM for most people, which makes communication difficult and time-consuming. Sometimes it is *very* onerous to find a connection causing a voltage when it isn't an obvious wire. And additional confusion arises because there are two extreme camps when it comes to bonding, bond everything vs bond as little as possible, both of which work, as well as the intermediate variations.
Starting with vocabulary, "ground" is earth, zero potential, the water your boat floats in. Your DC negative bus is your electrical system's common ground by being connected to your engine, or somehow connected to the water if you don't have an engine. "Bonding" is used for the system with zincs and green wires protecting your underwater metals, not the negative part of the DC electrical system (black wires).
Back to your rudder shaft, if it is stainless steel it absolutely must be bonded - as in connected to the zincs on your boat, and you DO NOT want it connected to your DC ground system. My rudder post is inaccessible at the moment so for comparison I just measured the voltage between my lightning ground, which I KNOW is 100% isolated from every system on my boat, and my stainless water tanks, which are not bonded, and I measured 0.26 V.
The next step is to check the resistance between the two, mine measured three mega ohms, which proves there is no connection between the two metals. So where does the voltage come from?? If you find out please let me know! If you have low resistance between your rudder shaft and DC ground system that means you do have a connection and you need to eliminate it. Additionally, your rudder shaft should be checked for corrosion - crevice and pitting (if it is stainless steel) from not being properly bonded, and stray current from being part of an unintended electrical circuit.
Your rudder shaft should be part of one circuit only: a green wire connecting it to the bonding system bus, which is connected to the zincs on the hull, then the water completes the connection from the zinc to the submerged part of the shaft. And confirming that there is only one connection can be difficult - as you noticed, the rudder shaft is connected to the steering system, which is connected to the pedestal, which over the past few years have more electronics mounted on them than the Apollo rockets of the 1960s.
On a related tangent, it is commonly said that bonding connections should have less than one ohm of resistance, but I think one ohm a lot of resistance for a bonding system. Every bonded metal in my boat has 0.1 ohm of resistance between it and the bonding bus. You need to haul your boat to check the outside connections between the hull zinc and the protected metals, and those should also be less than 1 ohm, preferably much less. Assuming a clean, properly connected bonding system, that measurement is actually the resistance between the bonding system bus and the zincs on the hull.