It's in the 4002-6000 service manual schematic (a little bit hard to follow with tired eyes, but anyway...)
L and R outputs from the pickup should go to pins 9 and 1, respectively, on the internal connector. These are the pins that are at the ends of the arc. Pickup signal grounds go to pin 7 and shield ground to pin 5 (middle). I suppose the pins would be numbered in the connector,
but if not, you can probably tell the ground/shield from the others. The pickup signal ground should go to pin 2 in the outside DIN and the shield ground to the cable shield / DIN connector sleeve. L and R are 3 and 5 on the outside DIN.
Double check with the schematic anyway - the DIN cord from the outside world is on the general schematic page, and then the signals are routed through the muting relay board to the pickup (so there should actually be two pairs of these connectors inside). The latter board is described on the same page with the CD4 decoder. Your problem might also be on this board.
BTW the connector inside isn't actually called DIN - I suppose it's
"Noval", or the same connector that was used as tube/valve sockets.