I just purchased an LED transformer from a yard sale that I hope to use to supply power for lights for buildings on my layout.
Has anyone found a good source for the taps or a way to tap into the underground garden wire for running wire to the buildings? Can I use a string of LED Christmas lights for the bulbs and sockets?
I use suitcase connectors - you can get them at your local hardware store or home improvement store. there are also ones for tapping both wires of the cord, but they are more expensive.
Thanks Steve. I didn’t know what a suitcase connector was until I looked it up in Google and then I read a great description by “Steve”! . I used them on the Suburban and our trucks but never thought about them for the railroad!
The first time I heard “suitcase connector,” I immediately thought of the commuter run between Sacramento and San Francisco. 
I don’t know if this will help or not, but where the bulbs (I guess LEDs in your case) connect to the feeder wires off of the underground power supply, I use alligator clips.
This way I can easy lift and remove the building and light housing without having to undo underground wiring. A big plus when, like us, you take in all of the structures for the winter time.
We use Malibu wiring, a 300 Watt Malibu transformer/timer, and 4, 7, or 11 Watt bulbs (depending on the size of the structure). We even found a red bulb for the, well red light district 
Malibu Low Voltage Light Systems ues a form of suit case connectors on their individual lights in their sets. I have found problems with these types of connections after a couple of years of being outside in our not totally dry environment of the Midwest, which can also include snow and rain. I have slowly replaced them with electrical twist caps as they have failed or what I’ve always known as “wire caps”. Do they work without failure or flaws? No, but they sure are a lot eaiser to trace and repair. Just strip the wires back about an inch, twist the wires clockwise together and then twist ut the proper size “wire nut” over the top of the splice. Hide under ground or under a rock.