any thin 2 core wire is fine really - solder the connections and cover with some heatshrink tubing.
you can see a QD someone made (and the blip internal wire diameter) here
http://www.timetriallingforum.co.uk/index.php?/topic/128160-etap-blip-hacks/
For my redshift aerobars I made removable blips from scratch drilling out dummy plugs and running 2 core wire to climb switches under tape on bar and via a 2 pole connector to waterproof momentaries at the end of the bars.
"time spent on reconnaissance is seldom wasted"
you can see a QD someone made (and the blip internal wire diameter) here
http://www.timetriallingforum.co.uk/index.php?/topic/128160-etap-blip-hacks/
For my redshift aerobars I made removable blips from scratch drilling out dummy plugs and running 2 core wire to climb switches under tape on bar and via a 2 pole connector to waterproof momentaries at the end of the bars.
"time spent on reconnaissance is seldom wasted"