Dell Precision T7400 (Late 2007) - Manual (Page 185)

Adding and Replacing Parts 185
11 Ensure that memory riser card 3 is above system-board connector
DIMM_3 and memory riser card 4 is above system-board connector
DIMM_4.
Align the notch on the bottom of each riser card with the crossbar in each
system-board connector.
12 Insert the riser cards into the connectors until both riser cards snap into
position.
NOTE: If a memory-riser power cable is not plugged in, the system will not boot.
13 Connect the power cables back into memory riser cards 3 and 4.
14 Ensure that memory riser card 1 is above system-board connector
DIMM_1 and memory riser card 2 is above system-board connector
DIMM_2.
Align the notch on the bottom of each riser card with the crossbar in each
system-board connector.
1 memory riser cards 1 and 2 2 memory riser cards 3 and 4
2
1