Trailer Connectors and Wiring "Change D"
Ditto on the trailer connectors. Admittedly, It was a terrible idea to run the 50A (600W) charging circuit from the alternator through the trailer plugs. This current is continuous, and, even without corrosion on the connectors, generates a lot of heat (not to mention a 70 or 100 A alternator!). The 21 A (250W) glow plug circuit is probably not ideal for the trailer connectors, but it is a momentary-use circuit, and not likely to generate much heat in one minute or less of use (even with a little corrosion). Pull these two circuits out (and also the black ground wire, which has to carry the full load of the engine panel), and I think the trailers connectors are fine (and pretty handy) for the remaining low-load circuits. Coat the pins lightly with dielectric grease (auto part store), tape around the connector to prevent moisture, and I think you're good to go.
Depending on the specifics of the boat, one other circuit that might need a little inspection is the purple (key-switched positive) circuit. On my boat, this wire went to 3 components: the alternator excitation circuit, the fuel pump, and the hour meter. The add-on splices to the original purple wire were in poor shape. I don't know what the amperage draw is on on a Facet fuel pump, but I wonder if it's a little high for this circuit. I've been considering a "Change D" (to add to Tom's excellent wiring modifications) and connecting the unused red-yellow wire (previously from the starter solenoid in Tom's "Change B") to the "on" position of the key switch and then directly to the fuel pump. This would leave the purple wire powering only the alternator excitation and hour-meter circuits. Any comments?
Added: I just looked up the Facet 476459E fuel pump. It says average draw is 1.6A. I suppose amperage varies between pump start-up and continuous operation, and may also differ depending on whether the engine running or not (fuel flowing to the injectors vs fuel just being pumped through the return line). I wonder if it's a bad idea to have the alternator excitation circuit sharing the purple wire with a varying-load fuel pump, even if the total amperage is not a problem.