If you are using Lionel O gauge FasTrack, Please do not solder wires to the rails. Almost every section of O gauge FasTrack has one or two pairs of male connectors on the bottom. Attach your wires to female connectors and slide the female connectors and wire onto the male connectors built into FasTrack.
Here is a tutorial I found on it for the uno, but I've also recently found this one which cuts down on the need to use controller emulators for some games like sfv and xrd since it gives off xinput, the only catch is you need to have a board with native usb support and lose ps3 compatibility, but then again the ps3 is almost dead so I don't think anyone would care if it loses compatibility.
Also, I personally recommend just buying jumper wires and making the quick disconnect wires yourself with something like this, it easier imo since it doesn't need to be soldered.
I usually end up replacing stock connectors at some point with "quick disconnect" .110" 22-18 awg terminals (about 60% sure they're the same design)
Interesting tricks to these.
Edit: for the love of the Airsoft gods. Don't do any of this with a plugged in battery. I figure I wouldn't need to say this, but then came to my senses and figured I'd have to say it at least once. And remember, if the gun starts autoshooting or heating up UNPLUG THE BATTERY don't try to touch the baseplate or contacts.
Take the vinyl shroud off (colored cap that goes over the base)
Strip a small portion of the wire and slip the bottom part of the connector over it.
Use a pair of electrical crimpers and crimp the wiring part FLAT. (Here is the trick, it has to be completely flat to ensure you can bend the head of the terminal at a 90 degree angle. I always wondered what was up with this because I had accidentally let the crimping pieces overlap instead of flattening just about every time, and kept having to solder to keep the terminal from disconnecting from the wire which introduced other issues...doy. You'll know it was crimped correctly if you try to tug that sucker off and it doesn't come off.)
Slide some heat shrink tubing over the entire assembly while still unbent. (heat shrink tubing is important boys and girls...touch negative and positive somehow and poof....burnt wiring and battery. Still think you're okay? Nope...that baseplate be metal. And that metal touches your connectors. Use heat shrink tubing.)
Bend the connector, should now be super easy to bend at 90 degrees without worrying about snapping it.
By default, the connection part of the terminal will need a slight amount of separation to allow a motor contact to slide in. Wedge in a thin flathead slightly, and pry it gently until the lip of the terminal contact is wide enough to accept the motor terminal. (The key part at this juncture is to pry the entry of the terminal lips wider than the rest of the part the motor contact slides into, not to jam the screwdriver in there to try to widen the entire connection area).
Should now fit perfectly, come off when necessary, but not disconnect when you don't want it to (wiring length also plays a part...so if you have many other problems, it might be the placement of wiring, the length or even the baseplate.)
An interesting note: I stopped soldering my motor contacts a while ago after discovering I had not been crimping the contacts correctly (again...when crimped the terminal wiring section should be FLAT) which increased the number if issues I was having with motor contacts.
Also interesting, seems the soldering caused more resistance when applied (might have been an artifact of the particular solder I was using). The crimp only technique has been very successful so far, and I've yet to have one yanked off since switching, so win win.