You need to remove curtains, take down track, run cord from overlap arm through pulley back under underlap arm through the pulley at the other end, leaving enough slack so cord hangs down far enough to be able to pull, back to under lap arm. attach cord to both overlap arm and tie off ends to underlap arm. replace track, rehang curtains.
malcolm
May 2011
http://www.orrsys.co.uk/electronics/curtains.html
This link gives you a diagram and instructions. I found the simple diagram enough to work out how to rethread a cord pull . Good luck.
paul
January 2011
I can answer this question...
My cord on my curtain track has come undone. How do I rethread it?