Dell Latitude 5424 Rugged Owner's Manual page 137

3 Tighten the two cap screws on the serial port [1] in the rear I/O space.
4 Connect the I/O board FPC [2] to the system board and then to I/O board itself [3] and secure it using a piece of tape [3].
5 Install the:
a PCIe heatsink fan assembly
b WWAN card
c WLAN card
d Bottom chassis cover
e Batteries
6 Follow the procedure in After working inside your computer.
Removing and installing components 137