I got the idea for this from Leah Buechley's LED sequins made with crimp beads. I wanted to solder thread connections instead of sewing. I like the flexibility and durability of stainless steel thread but it doesn't solder.* So I developed a "work-around."
I couldn't solder to the thread, but I could solder around it. The trick? String a crimp bead onto the thread, then melt solder into the bead hole. If there's enough solder, the bead stays put. It's easy, and you can add a soldered bead even if you don't have access to the end of the thread (i.e. because the thread is already attached to something).
a needle threader
conductive thread - I'm using Adafruit's 3 ply stainless steel thread.
crimp beads - Choose a size that leaves a bit of a gap between the thread and the bead. For this thread, I'm using #2 beads.
solder (thin enough to fit inside the bead)
stand for holding soldering iron
Keep in mind, when you heat the bead up again, the solder inside will melt. If it leaks out, you may need a "refill".