Dell Precision T7400 (Late 2007) - Manual (Page 192)

192 Adding and Replacing Parts
10 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.
11 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.
12 Connect the power cables to memory riser cards 3 and 4.
13 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 power connectors 2 connector
3 securing clips (2)
3
2
1