Sailboats have an especially high incidence of electrical terminal corrosion at the mast step. Some professionals advocate making up all wire-to-wire connections in a waterproof plastic box. I personally disagree, as there is really no such thing as a totally waterproof enclosure. They all leak at some point and the internal splices or terminal connections do end up corroding.
So what’s the answer?
I’ve found the best way is to fasten a terminal strip to a stringer next to the mast step and using ring terminals, not the fork ones, make up the connections on the strip. Why ring vs. the fork terminals? The ring terminals won’t work loose. Just be careful not to drop a screw in the bilge. Bilges have these little creatures that eat loose screws. They have to exist as I’ve never been able to recover one after its been dropped.
An important thing to note
If the cable or wire harness exits the mast through a rough hole, you will have big problems down the road. The wiring will eventually chafe and you will have a major job re-running the damaged wires in the mast. Trust me, you don’t want to have to do this as it could end up costing you several thousand dollars to fix what a $2.00 rubber grommet would have prevented. The rubber grommets can be found in any electrical supply shop, i.e. Granger, RadioShack.
Back to the wiring connections!
After you’ve tightened the screws, coat all the surfaces with a dielectric spray or coating such as ECK. A word about ECK! It’s a coating applied to prevent galvanic action with all dissimilar metals including stainless steel, aluminum, copper and brass. It should be reapplied every time the terminals are disconnected and then re-connected. Make sure that the wires leading to the terminals are properly fastened to the stringer, or bulkhead as in the case of deck stepped mast. Never let loose wires dangle from a terminal strip. You’re just asking for problems.