Here are some tips for soldering these connectors:
1. Use a low melting point solder. We use electrical repair solder that is 60% tin and 40% lead with rosin flux core. This is available at most hardware stores.
2. Use a HOT soldering iron. A soldering iron with a low heat output makes it really difficult to get a good bond between the two surfaces.
3. Plug the T-Plugs together before soldering. Plugging them together helps dissipate the heat, plus holds the prongs in position.
4. Apply solder to to both surfaces before joining them together. This is called 'tinning", and it's the key to getting a proper bond between the two surfaces. Once you have tinned each surface, hold the surfaces together and apply heat with a HOT soldering iron. The solder on both surfaces will melt together, forming a secure bond.
5. Remember to slip a short length of shrink tube onto the wire you are connecting to a T-Plug before soldering, and keep it as far from the point of soldering as possible. Once the soldered connection has cooled, slip the shrink tube into place and use the heat from the soldering iron, or the flame from a candle, to shrink it.
6. Consider purchasing a Soldering Jig and/or a packet of EZ Solder Couplers. They make the job of soldering so much easier!