If you're a subscriber to the Yahoo T-Trak group, you may have noticed that the topic of wiring erupts into heated discussions from time to time. Let's try and sort the situation out as best as we can….
Wiring a small layout for DC operation
For a basic T-Trak setup, the T-Trak Data Sheet tells you everything you need to know. One module has a pair of feeder wires for each track. Install Kato's feeders with the blue wires to the outside rails. The blue-white-white-blue feeder arrangement has been the convention since the beginning of T-Trak. (You could argue with it — and people do — but that's about as productive as putting your hot-water faucet on the right side of the sink.) Connect each pair of feeders to the appropriate terminals on your power packs, and you're done.
If you find that trains move in the opposite direction of what the direction switch on your power pack indicates, just reverse the wires.
Wiring a small layout for DCC
Because DCC enables you to run multiple trains independently from the same power source, there's no need to have separated loops of track to easily run multiple trains. If any of your modules have crossovers, you'll need to make sure that the polarity matches between both sets of rails, otherwise the whole system shorts out when a train crosses from one track to the other. Flip the feeder wires for one track, and connect them white-to-blue and blue-to-white at the power supply.
Wiring a larger layout
Here's where things get complicated. The T-Trak standard specifies an arrangement for a single set of feeders. Any layout too large to fit on 1-2 folding tables will need more, to ensure good electrical continuity. The polarities on all feeders to each track must match. If tracks are interconnected, polarities between tracks must match, also. To carry track power long distances across a large layout, heavier wiring is needed to minimize voltage drop. (Kato's feeders are 24AWG, which is fine for short distances.)
All the feeders are tied together with a bus wire. Since the T-Trak standards include no bus-wire specification, some groups have gone ahead and formulated their own. Northern Virginia NTRAK's T-TRAK Division's specification is a good place to start. The Northwest Georgia T-TRAK specification, authored by Jim Nealand, is another one in use. The North Raleigh Model Railroad Club has a very comprehensive document as well. There are others out there, too (we'll add more links as opportunity permits).