So I just went through this with my bike making nearly the EXACT same symptoms ... what ... perhaps 3-4 weeks ago.
Turn on key, could get sweep, lights, hit the go button, just a little clicking. Much like a dead battery.
After some messing about, I found that holding the wires under the switch in a particular orientation allowed the bike to start. Unfortunately, holding the wires whilst driving was not convenient for me.
Try jiggling them around or holding them forward, back, left, or right, and see if one of those allows the bike to start. I bet it will.
Either way, I'm personally gonna say I'm 90% sure its your ignition switch. Especially where you had issues with it and soldered it previously. I bet you have a short in there.
Triumph replaced mine on good will. They covered the parts, but not labour. So I just installed it myself. Just ask your dealer to inquire about a good will warranty exchange for you.