type
  TMyThread = class(TThread)
  private
    FStart: TEvent;
  protected
    procedure Execute; override;
  public
    procedure StartNow();
  end;

implementation

procedure TMyThread.Execute;
begin

  FStart := TEvent.Create(nil, false, false, '');

  while not Terminated do
  begin
    //--- Auf StartEvent warten
    FStart.WaitFor(INFINITE);
    ...
    ...
  end;
end;

procedure TSweepThread.StartNow;
begin
  FStart.SetEvent;
end;