Has anyone replaced a 3 wire alternator that is connected to a voltage regulator to a single wire alternator? Anything I need to be aware of or think through? 

Current setup: Ford 302 Engine Reverse Rotation with a 4 speakers and bluetooth sound deck. 

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There are a few things to keep in mind

The lower mounting hole in the Delco will need to be drilled out to 7/16 inch to let the original mounting bolt for the Prestolite fit

You may have some minor shimming for alignment

With the one wire, you hook your present Orange wire to the output terminal and then there's a provision for a ground wire from the alternator to the block etc. Some people use the ground wire, others don't because it's grounded to the block through the metal mounting bracket.

You want a marine Delco that has flame arrestor screens front and rear.

Your original setup has a 37ish amp alternator and an ammeter in the dash. All of the charging current goes from the alternator up to the dash and back to the starter solenoid and then to the battery and the wire is sized to handle the full 37 amps

If you put a big honkin' 100 plus amp alternator in the boat, you'll have plenty of capability of starting a fire.

If you get something like a 63 amp which is about as small as they make in a marine Delco and put a 40 amp breaker or fuse on it's output your wiring will be protected. Or you can run heavier wire up to the dash and back to the starter solenoid

If you google 400-20012 or click on the link below you'll find a 63 amp, marine one wire Delco at a variety places at a variety of prices 

http://www.google.com/search?q=400-20012&oq=400-20012&aqs=chrome.0.69i59j6j69i60j69i61.6359j0j7&sourceid=chrome&ie=UTF-8" rel="nofollow - link

You can cut the unused wires for the old voltage regulator and alternator ( the excitation and sensing wires) or leave them in place with the ends taped.

If you want to use all the available amps and have a working ammeter, then you need heavier wiring up to the dash, through the key switch Batt terminal and back to the starter solenoid.

Here's a good representative wiring diagram for your 77 engine assuming it's a PCM and not a Commander.

If you want to get rid of the ammeter, the diagram tells you what to do with the Orange wire (run it to the solenoid and unhook the end at the ammeter and tape it)

If you want to keep it simple, do the 40 or 50 amp fuse with the orange wire hooked up at the end by the finely manicured thumb