Re: CJ- ALT, 3 wire to 1 wire ???
Whenever there's current running through a conductor there's a voltage drop across that cable. The end opposite from the alternator will be a tad lower than at the alternator.
A battery that's only partially charged has very near the same voltage as one that's fully charged - within thousandths of a volt, even the slightly lower voltage at the battery end "seen" by the regulator results in the regular "thinking" the battery needs more, so it keeps on charging it. (Remember the energy being pumped into the battery is being converted to chemical energy, not stored voltage. That's why the voltage is so close.)
If it's "seeing" something other than the battery, like the alternator output, it gets "tricked" into thinking the battery's fully charged and lowers the current.
It eventually drops down to the point where the only output current it's providing is what the rest of the system demands, lights, ignition etc. The battery only gets "what's left over."
Remember too that a battery can only accept about 30 Amps to charge, more than that takes way excessive charging voltage and will kill the battery. When you gut up into the 16+ volt range it's possible to overcharge and burn it.
Keeping a battery undercharged shortens it's life and can't provide as much energy that you think it can. Like when operating a winch, you want as much power as you can.
Try it - Discharge the battery part way - like crank it a long time, or leave the lights on for awhile.
Attach the sense line to the alternator output - the cheat method - like the one wire's.
Run it till you think it's charged. Check the specific gravity of the battery - remember the reading.
Now change the sense line direct to the battery.
Start it again. Hear the alternator groaning again? It's charging that "fully charged battery."
After it's charged again, check the specific gravity again. Higher now. Battery is happier.
Believe it or not - The energy is actually stored as weight - the battery actually gets heavier! Not enough to notice, very slight, but enough to measure with a precision scale - try it! The higher specific gravity proves that - the higher the number, the heavier the solution is.
When a battery charges up, the electrical energy is stored in it chemically. That's why they say never add acid to a battery that's low - just water. If you did, the acid content would be too strong and the plates would erode real fast, and the chemical reaction would not work as well.
The sulfuric "acid" you buy at the parts house is dilute acid already, not full strength sulfuric, already has the right mixture of acid to water.
Since the energy is converted to chemical energy, the voltage is very close comparing a partially discharged vs. a fully charged one. The regulator makes it's determination as to charge or not charge by that very slight voltge difference.
Even a very discharged battery still has 2.1 volts per cell, but very little energy left.