The 1979 200D with pull knob has no relay.

Here you can see how you should wire the glow plug. One wire as an input, the other one an output, with an insulator between them.



Here you can see the entire engine, but it looks slightly differently, as this is a key starter, with a relay and without the thermo-time switch.



But your glowers look like pencil glowers to me, but take one out to confirm. It is important, as the wiring is entirely different for pencil or loop glowers.