Connectors on the backplane?

Is the 400 running OK with the card installed? If so, and you've got the Gauge Series, run the included SlotInfo utility to see if there's a Declaration ROM on the Card that will tell you what it is..

TattleTech is another good ROM Card Spelunking utility. You can run the PDS/NuBus report (IIRC?) individually and it will usually be able to tell you more even than SlotInfo can about a card in either type of slot.