If you do any driving at night the one wire alt. won't be sufficient.
You should use 10 ga wire minimum to the junction block and should run a voltage sensing wire from the 3 wire alt. to it.
There will be a considerable voltage drop in the 5-6 ft. of wire to the block then an even more considerable voltage drop when you turn on the headlights. The one wire alt is sensing from itself and it doesn't notice these drops so it doesn't compensate for them. With a sense wire at the juction block it will notice it and compensate for it.
