Please note that some lamps that are made in sections have very small wireways at both ends of the tube and have large spaces between these holes. It is almost impossible to thread anything larger than a standard 18-2 SPT1 wire through them. If you take then apart (unscrew them) you will have better luck getting the wire through the holes.
It is necessary to fully disassemble the lamp to feed the wire from the bottom of the lamp. Use a wire (thin but stiff) inserted from the top of each section downward and through the bottom hole. Strip a section of both conductors to allow you to attach the copper stranded wire to the stiff guide wire and pull it through. Do this for each section untill you reach the bulb holder. Cut off the stripped section that you used to pull the cord through and then correctly connect the lamp holder. If there is space make sure you use an Underwriters Knot to prevent tension from being applied to the lamp holder connections when you reassemble the lamp or when the cord is pulled from the bottom of the lamp.
Reassemble the lamp from the top down, Please note that you do not want to simply turn each section into the other as this will twist the wire and weaken it. If it takes 6 complete rotations of the section to fully thread into the section above... rotate the section six turns in the opposite direction before screwing it in. This will prevent the cord from being twisted. Pull the cord tight between sections. Continue untill fully assembled.
Replace any busing where the cord goes through the lamp base as the sharp metal can cut the wire over time.
Attach the plug at the end.
Using a continuity tester ... test for continuity and for switch functionality.
Insert the bulb, any safety covers.
Not holding the lamp... Plug it in. Turn it on.