When I referred to the last fuel injector, this is what I meant (I definately don't mean to be patronizing with the detail):
If I'm sitting behind the steering wheel in my 300CD-Ts, the five cylinders run in a straight line from the grille (essentially) to the firewall. For the fuel injector closest to the firewall, since there isn't another injector to daisy-chain to, it's "output port" (for lack of a better term) should be fitted with the plug that, upon closer inspection, seems to be about a 1" long piece of the standard fabric covered fuel hose with a metal plug, slug, whatever you want to call it, stuck inside. This thus prevents fuel from squirting out.
Hope that clarifies it better.