"Solid". But it's hard to find stranded wire that small. Not that thirty gauge doesn't seem to me too thin to handle motor power. But lots and lots of guys would know better than me, because the standards I operate by are too old school and HO-hum. The old solid core wire did break. But it seems to have taken a few decades to do it. You slaps down your solder and you takes what you gets. That said, I'd use aluminum wire. I don't know what that gray metal is you're soldering to, but it could react to copper over time. Is aluminum wire less flexible? Everything's a tradeoff.
IDE ribbon cables off of old cumputers have some really small wires in them. They are individual stranded wires. I have some of those cables that have 80 wires per ribbon ! I used about 14 wires off a ribbon cable while making my cell tower. .
If not mentioned here already cheap earbuds have thin flexible wires. I am using some to route power between a gas electric critter and a trailer car.
I disassembled the trucks from one engine. Using my new 5 watt soldering iron, that works great, removed the old wire. Intend to use a door bell insulated wire which was heavier than the original. Regards, DMK
Why mess around? Just go to eBay and get the wire I pointed to. If that door bell wire is thicker/stiffer than the original (I knew it would be), you'll be sorry. Doug
ESU makes 36AWG multi stranded wire and with a current rating of 2A it's more than enough for an n scale engine.
Following the repair, I examined the electrical pickup path to the motor through the wheels to truck connection and determined it to be poor. I tested repair and the continuity was poor. I emailed Atlas asking if they had a better truck assembly.
With these locomotives having been last produced forty years ago, Atlas would likely not have parts and these would not be interchangeable with more modern designs. If you want to pursue, your best bet is to ask if anyone has parts on our Swap Meet section here or to keep an eye on eBay. I just checked my stuff and have no spares. Amusingly, I see wired trucks from the early days of N Scale, followed by their elimination for 35 years and now confounded wires are again reappearing in new locomotives such as Atlas' SD-35.
Made the solder repair but do not have continuity from wheels to motor. Gave up. Will use one shell for a dummy and he other shell on a replacement frame. DMK
Next time you're looking for used Alco FA/FB locos, choose the Life-Like/Walthers models made from 2000+. http://www.spookshow.net/loco/llalcof.html
Most of the DCC suppliers have very flexible with in gauge that will probably work for this. These are stranded as you want.
