Newbie question about wiring (HO) track

Yep. You got it.

However the locos will need to be evenly matched or the throttle might "turtle" one and "rabbit" the other.

You could use a few diodes to even them up some.  Each eats about .75v. in series (inline) .    Ive made throttle control for constant power supplies that way.  Put them on a switch and you could swap which train goes on which line.

So you can reverse, you need a pair, bands opposed, legs connected. Each will handle the opposing dc+ or dc- while the other does nothing. The pairs can then be stacked in series with the same drop rate as singles.

  One diode limits you to one polarity setting. Reverse toggle will then only work on one setting.

A bridge rectifier is four diodes in one package, arranged to make dc from ac. But they can be wired to give your dc a 1.5v drop vs two in series if you like the packaging or price. (all are cheap at a supply house)

Another consideration is how big a draw two locos are, vs how big your powerpack is. You want the supply to push about 20% more than the trains use. (in amps,voltamps,watts, etc)   and don't forget to add power used by passenger cars, track accessories (lamps, motors etc)

Use general purpose diodes with a rating above what your power supply has.

(double the voltage over supply max. Amps; the larger number handles more draw; overkill just means the diodes stay cooler. Close matches get much hotter (150°-180°... ouch, "I got blisters on me fingers" (a Beatle quote))

Thanks!  I'm gonna go ahead and pretend to understand the diode stuff for now, and come back to it later...

The Silverball Express is now a system

If you're asking if you can power both loops from the same power pack with one pair of wires reversed, so trains on two loops run in the opposite direction to each other the answer is YES.  Forget about diodes.

I did the same thing way back when in the olden days when all I had was two HO sets: an Athearn passenger set on the outside loop, a Marx freight set on the inside loop.

However, you won't have independent control of each train.  They will both respond to your throttle at the same time; Start, Stop and run at approximately the same speed depending on the locomotives.

It would be better to pick up a second power pack for your new loop, which would allow for independent control of each loop.

Rusty

UPDATE:  I missed seeing your video as you've already accomplished your goal.  But I still would recommend a second power pack for independent control.