I added lights and a motor to an OLD Athearn (replaced the rubber bands). I used heat shrink tubing. it was the easiest solution I found. It works great and hasn't failed yet.
Try to stick to brass rod about .019/.020" od. Be sure to clean it with some 400-600 grit emory paper and use some flux to make a good join. Tichy sell phosphorbronze wire which is even stiffer and solders just as well or better. The smaller sizes of pb wire (.010-.015") have good springiness and work well as wipers for electrical pickup.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
I get it, the light pipe is attatched to the shell. In the Kato unit I did they were not.
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum
Doing a similar thing in a Kato loco, I used heat shrink tube to connect the LED to the light pipe and then used just regular flexible wire.
You won't be able to solder to the piano wire. It's made of carbon steel. That's why people use brass rod for such applications. You can solder to brass.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
Piano wire is tempered steel and extremely difficult to solder, so you should try to use brass rod instead.