It sounds like you are starting with an internally regulated alternator but not a "one wire" since you have the two light terminals. True one wire turns itself on when it starts spinning w/o ignition input.
One terminal is ignition switch on... need to Google it to find out which. Coil + w/o ballast should work though more direct connection to ignition + may be less noisy and better. The other, I believe, is for remote sensing. You can use it to sense from the factory location (# 1 splice), another location like the fender relay or just jump it to the main output stud. Neither of the wires needs to be heavy. 14 gauge is more than enough.
Diode is normally not needed unless you are running an alt light. Again need to google it.
