Near-impossible for me to describe properly without a diagram. If this Beogram is new to you the service manual downloadable here is well worth it because it shows how to set up the tonearm properly and everything else - including the circuit diagram that'll answer your question.
I find that soldering a DIN plug is fraught with hassle because the plastic that hold the pins tends to soften under heat and the pins end up skewed - plugging it into a socket before I begin is the workaround I use for my poor soldering technique. I had the same problem as you with my Beogram, and I found it a lot easier to replace the entire lead with a ready-made extension cable from Maplin - I cut off the line socket and stripped the wire ends and soldered them into the Beogram.
Cheers, Steve