Re: Wiring problem: solder not adhering to miniswitch...
Pierre, you should be OK without it. Try it out. If you have to, and you should anyway, shield the cavity with aluminum foil and spray glue. There's some sites on the net about doing this very thing. Guitarnuts.com is one, Projectguitar.com is another.
Sabe made a good point too, make sure you have enough flux there. You should use 60/40 rosin core solder, or 63/37 rosin core. The rosin acts as flux to help the solder adhere.