Правильное подключение

procedure TfrmMain.Button1Click(Sender: TObject);
var
  DB_FileName: string;
begin
  with TOpenDialog.Create(Application) do
    try
     InitialDir := ExtractFilePath(Application.ExeName);
     Filter := 'Access DB Files (*.mdb)|*.MDB';
     if Execute then
        DB_FileName := FileName;
    finally
      Free;
    end;
  if DB_FileName>'' then
    try
     ADOConnection1.ConnectionString := 'Provider=Microsoft.Jet.OLEDB.4.0; '+
                               'Persist Security Info=False; Data Source='+DB_FileName;
     ADOConnection1.Open;
    except
     ShowMessage('Ошибка открытия БД '+DB_FileName); 
    end;
end;

if OpenDialog1.Execute then
begin
DataModule1.ADOConnection1.close;
DataModule1.ADOConnection1.ConnectionString:=
'Provider=Microsoft.Jet.OLEDB.4.0;'+
'Data Source='+OpenDialog1.FileName+
';Persist Security Info=false';
DataModule1.ADOConnection1.Open;
end;

const
  Provider   = 'Provider=Microsoft.Jet.OLEDB.4.0;';
  PersistSI  = 'Persist Security Info=False';
  DataSource = 'Data Source=%s;';
  
procedure T_afw_main._op_fileClick(Sender: TObject);
begin
  _op_dlg_.DefaultExt := '.mdb';
  _op_dlg_.Filter := 'Access File|*.mdb';
  _op_dlg_.Execute();
  if FileExists(_op_dlg_.FileName) then
  begin
    _cnt_.Connected := false;
    _cnt_.ConnectionString := Provider + Format(DataSource,[_op_dlg_.FileName]) + PersistSI;
    _cnt_.Connected := true;
  end;
end;

И это кусочек на скорую руку