Use crimp connectors. There are bendable tines on the underside of the track for these. Slide the connector + wire over the tine. I used these or very similar. https://www.autozone.com/stere...-terminal/421754_0_0
The key is getting the exact right sized ones and unfortunately I'm not near my box of them ... so this is a guess. You can search ogr on this topic because it's come up before and some folks know the exact size. [ note these are available at places like digikey etc...]
As for the wire diameters. I made it work. I'm not sure I used 12 gauge, maybe 14. Even that's a tight fit on these. Well I made it work. I'm not sure that big gauge is needed or even 14.
While I used to have 100s of feet of fastrack looped around in a say 20ish x 25ish space.... i don't any longer. But I found two flexible wires twisted together with crimps on the end the easiest to deal with and hide under the track. I bought one spool of this on a whim pre-made somewhere... but i also made my own with a vice holding the ends of two wires and a drill on the other... anyway can't say i really recommend that approach but it did work and produced some twisted together wire that stayed that way.
After that I just went out from one of those breakout strips -- you can buy these from MTH or they make no frills one and sell them at home depot.
All I did was run wire on a need to basis from the break out. Since my layout was temporary in nature I favored flexibility first and on the carpet.
Then, I found if I ran a conventional engine very slowly around the track set at minimal transformer power it was easy to see the weak power spots or even dead spots.
I'd either run a long set of wires from from breakout or jump from another track piece. Either way I got good enough power to do what I wanted. And I could tear it all up with ease.
Two other observations. i found that reliability improved with 30" straights vs many 10" straights or smaller. But the price is that it very easy to snap the diecast connecting tines because of the longer leverage of 30" track when dissembling.
So take care there, there's no place to get replacement tines except another track piece or you can jump from another track piece using the bendable tines on the under side.
Legacy and dcs worked fine after all this.
