I did the alternator conversion on my '79 after the regulator fried. If you want to go ahead with the conversion (which gets rid of the external/mechanical regulator from '79 and '80, RX2, RX3 etc), you should pick up an alternator from an '81 to '85 (some Mazda trucks and 626's use the same one).

   Your old alternator will have a large main battery lead, and a four connector plug which goes to the regulator. The new alternator will have the same large main battery lead and a three connector plug.

   The Haynes manual diagrams are pretty good, so make sure you have them handy. The modification is as follows:

Theory:

   The old external regulator has a circuit in it so that when the alternator is producing power, it enables the choke/electric carb heat system and if the alternator is not producing power (either broken or the engine off) the dash lights come on and the carb heat is off.

   The three connector plug on the new alternator is

1. Ground
2. Ignition power
3. Dash light

Solution:

1. Ground is simple.
2. Ignition power goes to a fused ignition source (most likely before the balast resistor for the ignition coil).
3. Wire from the alternator "Dash light" output will go to a standard automotive relay (you'll need to buy that) so that if the alternator dash light line has 12 volts then the car's dash light line is grounded (or if the alternator dash light line is 0 volts then the choke relay line is grounded).

   You may reuse all of the lines in the harness which go from the old alternator to the regulator. I can't check what I did because my '79 is covered, in a barn and baracaded with snow.

   Hope that helps. E-mail if you have any questions.