If you haven't already secured the lighted items on the layout, the place to solder extension wires to those 6" leads is the workbench, not standing on your head under the benchwork.
You have mentioned multiple DC transformers - does each have a separate bus (I hope!) Is there only one 'common return' bus (Like common rail for analog DC loco control?) Or are you gang-loading all of them onto common positive and common negative busses? (Hey, Joe, where's that electrical rated fire extinguisher?!!!)
My practice is to use extension wires long enough to reach terminal blocks installed just behind the fascia, where I do my wiring while seated in a chair in the aisleway. Like you, I use multiple transformers (AC - lamps aren't polarity sensitive and diodes will sort things out for themselves) wiring each as a separate entity. I may also subdivide the several parallel circuits on each and switch some individually - street lights stay on all night, but Jiro Salaryman needs his sleep. (He and his family also wake up pre-dawn, since dawn comes late this far west of Tokyo.)
Fixed layout lighting is a model that can contribute a lot to the layout's ambiance if a little thought is given to how lights work in the real world. One size, and one toggle switch, does not fit all.
Chuck (Modeling Central Japan in September, 1964)
Get used to soldering.
Once you're under there, and the iron is hot, soldering a whole bunch of connections doesn't take much more time than soldering just a couple.
Terminal blocks, on the other hand, are fine for one or two connections, but when you try to put a lot of wires on one terminal, or daisy-chain connections, it can take longer than soldering the whole batch.
It takes an iron man to play with a toy iron horse.
You could solder longer leads to each accessory at the bench before you install it (no upside-down soldering) and then use terminal strips under the layout. With longer wires, a bunch of lights could all connect to a single common point for attachment to the power bus, yet with terminal strips (the screw kind), you could pull one out for repair without cutting or unsoldering anything.
It's not much of a shortcut - 30 lights is 60 wires that have to be connected no matter how you end up doing it. Run the light bulbs at 75-80% of their rated voltage, and they'll look better, melt less palstic, and probably last your lifetime. That's about 9 volts for a 12 volt bulb, 12 volts for a 16 volt bulb. With multiple power supplies you'll need multiple buses. Which also makes sense as it would give you the ability to individual turn on various things independent of the others.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
You can buy a terminal block at Radio Shack for a couple of buck and hook up any wires that can reach it (6 inches is short).
If you are using Miller Engineering signs, they also sell a terminal block, but at a premium price.
Other than that I you are stuck soldering wires. Buy a mid-wire wire stripper and use that to create (non-overlapping) clear spots in the bus wire.
Co-owner of the proposed CT River Valley RR (HO scale) http://home.comcast.net/~docinct/CTRiverValleyRR/
I plan on having 30 lighted cars, 30 street lights, numerous lighted billboards, etc. I will have multiple DC transformers to power them all. My question is how do I attach the individual lighted units to the assessory buss? I was thinking of using suitcase connectors from the buss to a feeder wire and then soldering the feeder to the light but that's a lot of soldering! The two wires from each light fixture are about 6 inches so they wouldn't reach the buss directly. Any shortcuts for doing this backbreaking task???