Lighted MTH Dummies

That will depend on the dummy locomotive.  For instance, I have a Legacy lighted SD-80 that has Legacy control with directional lights, smoke, and electrocouplers.  I have other ones that just have track pickups and light bulbs.  The fact that the description mentions directional lights indicates that it either has a tether or some intelligence.

Have you popped the top off to see what's inside?

MTH dummies are nothing more than engine shaped boxcars. The lit ones just have rollers, a constant voltage light board and an on/off switch to control the lights. The "directional" light ones have a second switch on the bottom so that you can select which end of the locomotive the headlight illuminates. There is no other electronics in them.

Have the same engine in Pennsy and it stays constantly lit anytime the power is on...

That's pretty simple, I didn't realize that "directional" meant you always had to run in the same direction until you flipped the switch, that's pretty lame!

When I do DCS upgrades, I make the dummy actually have "directional" lights, and you don't have to turn it upside down to change directions!

No I have not purchased it just yet.  But from what I am reading it looks like it will alight when simply placed on a powered piece of track which is what I want.  Thanks for your kind responses.  Merry Christmas!