Where does the lead wire for the voltage regulator hook up?

SOURCE: the wires going to the voltage regulator keep burning up.

Common problem with poor quality parts, the regulator is the problem, the generator is working other wise you would not have fried the wiring, you answered your own question. someone telling porkies to get more money from unsuspecting client?
The regulator controls the voltage not the generator, the generator only supplys the voltage it cannot overcharge unless the regulator is not working properly, simple!

SOURCE: which post is which on generator on a 1975 sportster?

the post should be the same as an original. The wires should be green and tan. Green wire goes to the post towards the front wheel and the tan to the post nearest the engine. Don't forget to "polarize" the generator before starting. procedure is in the service manual. Momentarily short between the battery positive post and the field terminal.

SOURCE: Melted wire hareness leading from the Stator to Regulator

Join the Honda Ricers Club ... you can get the service manual on line as a member - print it even.

SOURCE: connecting wire from regulator

The large wire from the voltage regulator goes to the Positive side of the battery. As an alternative, you can also connect it to the starter where the large cable comes from the battery positive terminal to the starter. I think that's where most Softail models have the regulator wire connected.

If you connect it to the starter, all this does it make it a bit easier to connect since the battery is inside the horseshoe type oil tank. Basically, you are using the battery cable as an extension cord to the battery to keep from having to fish the wire up to the battery.