A plug with three wires, a ground strap, and the battery line connection, right?
If so, internal regulator (what you plug the three slot plug into). If not, it's external like my 220D, but I'd be surprised. Dome diesel models have an overvoltage control relay that can play merry hell with the tach, etc (tach is driven off the alternator, I think, like the Volvo).
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!