On Mon, 15 Apr 2013 09:29:49 -0400, J Herring
wrote:

Do you own a multimeter? If not, get one.

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Buying a multimeter is good advice. It will pay for itself many
times over.

If you have multiple circuits failing it will probably turn out to be
a bad connection coming from, or returning to, your battery.

On the other hand the wiring, fuse panel and switches in a boat that
old are probably pretty well shot. Replacing all that is a non
trivial project but it will save you a lot of aggravation down the
road.