For track work I use a 40 watt iron with a large chisel point. This one is by Weller. I love this one for a very handy safety feature...it has a glowing orange light on it to let you know it is plugged up. I've left irons on many times.
I use liquid soldering flux for track work. It flows better and makes less of a mess than past fluxes.
This soldering iron needs to be cleaned and tinned, so we take the time to do it right. Sponge is wet and ready to go.
Using the marks made in purple I find the hole and drop the feeder wire or "drop" into the hole with the tinned "hook" at the top. For wiring I make the locomotive engineer's side red, and the other side white. This is part of the loop so the engineer is now going the other way, so white is closest to me. Goof this up and you are rewiring for hours!
Put a drop of flux where you want the solder joint to go, then heat it with the soldering iron and touch some silver solder to the web of the rail. If you do it right you'll get a nice, flat, shiny silver surface on the web of the rail.
Use a drop of alcohol and a cut down flux brush with stiff bristles to clean the track. This is a very important step because if you don't remove the flux it will migrate to the rail head and cause the electricity to slop conducting to the train. It can also corrode the track or wire later on.
There! A nice, shiny, soldering joint. Normally I would not do this on visible track, but since this is hidden I'd rather have a great bond than a small joint.
Clean the joins thoroughly!
Once the drops are soldered in, test them with a freight car. You should not get any bumps and the feeder wires should be OUTSIDE of the rails, not inside where they can hit the flanges.
If you need to label your wires, now is a good time to do so.
This piece of track has a little build up of corrosion on it, so I'll just file a clean spot for soldering.
More drops installed.
The frog on the Walther's turnout has a mounting lug on the side. We'll use that for adding the green wire. The green wire is 18 AWG gauge and won't fit through the whole, so I'll drill a 5/64th's hole next to it.
File off the black coating on the mounting lug so that you get a clean surface. Add flux and solder to tin it.
Pull the green wire through and solder its tip to the mounting lug on the frog.
With turnouts be extra careful and test using a test car to see if there is any interference from the soldering joint. Clean the track carefully around turnouts as to not damage them. The are delicate and expensive!
I finished up all the drops and thoroughly cleaned and checked the track. We're almost ready to run trains!