What gauge wire should I use? What kind of wattage and solder?
Thanks!!
Get very small gauge wire-wrap wire with kynar or teflon insulation. The amount of current on a keyboard is nearly zero, so wire gauge can be very (30 gauge) small. The insulation resists the high temperature of soldering quite well. If possible, get old style fluxed lead solder, as the silver stuff has a higher melting temperature, and is more difficult to solder, especially for beginners.
In the unlikely event that you are trying to re-wire a membrane board, these methods are useless; you cannot solder to the membrane, however, you are not out of luck.
Conductive thread and
conductive epoxy can also be used.