Assumption: (please check) mainboard PS is on blue cable, plugged into the left hand side of the BEL magnetics adapter, when looking tom the flying lead side.
power up as is, wait until networks up at 100Mb (LEDs or ethtool), disconnect blue ethernet cable to confirm we got it right, reconnect blue cable, now directly to Ethernet card in topotest1. check LEDs for 1000Mb.
colours in case we have wired blue cable as described above)


BEL  bl bn  ye or  rd bn  bl wt   that's working as is
pair + 4    + 3    + 2    + 1

-------------------------------------------

WE   4+ 4-           2+ 3+
            3- 2-            1+ 1-


 
 8 6 4 2
9 7 5 3




cable port polarity: + on 7 4 3 1 for pairs 4 3 2 1 in this order
                     - on 8 5 6 2
on pins    9  8  6  5  7  4  3  2
           4- 4+ 3- 3+ 2- 2+ 1- 1+