If the antenna is not installed, you will need to swap the display assembly for one having the leads.  You cannot disassemble the display assembly to install the antenna -- it's a fused together (with adhesive) single unit.
Hi,   I have 7760 without WWAN card and i'm planning to get it but i see in installation process there is 4 cables i think for antenna but where i can find them?   Thanks  
Dell Precision 7760 WWAN install