Soldering pickup tags to their leads.

[ppppenguin]

I wouldn't solder to a tag attached to any cartridge. What you need is a 3rd hand. I've got a less sophisticated version of this:
https://www.amazon.co.uk/SE-MZ101B-Helpi...B000RB38X8

You could probably improvise something with a croc clip, some stiff wire and mole grips.