procedure TForm1.Edit1KeyUp(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Length(edit1.text)=Edit1.MaxLength then
  begin
    SelectNext(Sender as TWinControl, True, True);
  end;

end;

간단하게 해본건데요...
이렇게하시면 잘될것이라 생각됩니다만...
혹시~ 안될지 모르니 참고하시기 바랍니다...^^


unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    Edit4: TEdit;
  private
    { Private declarations }
    procedure WMCommand(var Msg: TWMCommand); message WM_COMMAND;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.WMCommand(var Msg: TWMCommand);
begin
if Msg.NotifyCode = EN_MAXTEXT then
begin
   PostMessage(Handle, WM_NEXTDLGCTL,0, 0); // 다음 콘트롤로 focus 이동
   inherited;
end;
end;

end.