This info maybe elsewhere on the forum, but I've sorted out the normal AUX socket (simple plug with plastic cover in the console between the front seats) connection on my MFD3, with the
help of NickP, and it seems appropriate to record it on this thread.
On the original Seat CD/Radio the AUX cables (3 off - black earth, white and purple Left & Right feeds - can't remember which was which) were connected to the CD earth/L/R pins at the back of the unit, as identified from the pin out
sticker on the back of CD/Radio unit.
For the MFD3 these three cables need to be moved to the respective AUX pins as identified on the pin out
sticker on the back of the RNS510. Same blue connector block, just different pins - in fact the black earth pin is already in the correct position as the CD earth on the CD/Radio unit is now the AUX earth on the MFD3. Threrfore only the L & R feeds need to be moved to new pins, so move the L feed to the AUX L pin and the R feed to the AUX R pin, as identified on the RNS510
sticker.
I don't have a diagram of these pin confirgurations, but if you compare the two pin out
stickers it will all be clear.
To move the cable pins around in the blue connector block firstly release the blue connector from the main quad block connector then remove the outer blue sleeve by lifting the retaining tab on the side (a fingernail will do the job) and sliding the sleeve away from the black connector block beneath. Then select the cable pin you want to remove from the black block and press down gently (with a small screwdriver or ballpoint pen) on the lower of the two silver recesses at the pin position, and it should just unclip and slide out from the connector block. Move the pin to the new position on the block and slide down until it clicks home securely.
Then reassemble the blue connector and quad lock block and refit to the RNS510. The AUX socket between the seats should now be back to good sound quality at a normal volume level.
Many thanks to NickP for the above. Ian.