Frist off do not use plumbers solder or acid, Strip back the wire to leave no more than 1/8 of bare copper when inserted into the terminal end. coat the outside of the bare copper with rosin paste. Clamp the terminal end in a vise clamping as little as possable to avoid heat lost to the vise. heat the end and fill about 3/4 full of electrical solder. While the solder is liquid draw the torch back and heat the bottom so you burn the covering on the wire. Then slowly insert the wire into the end as the solder in absorbed into the wire, when the wire bottoms out remove the heat and let cool, if you continue heating the wire will wick up the solder and the wire will become hard and not flexable. the use a piece of heat shrink over the connection to help keep the acid out.
