Hello ALL ---
I have just installed LED lights in one train of my O-Scale 2-RAIL converted IRT R-21 Cars - See 11 Photos BELOW - replacing those dim incandescent bulbs they originally came with from MTH as 3-rail operated cars. These LED'S lights take only a fraction of current to operate all of them (60 lights over a 5 car train) and thus do not cause noticeable current loss-drop (ie: thus not acting like "resistors" ) to the traction motors as the MTH light bulbs did.
Now these cars have that florescent lighted look, color and brightness of the real R-type cars. I use 12 LED lights on a strip -- in strip-attached groups of 3 LEDS each group ( 3 + 3 + 3 + 3 ). They are GOO-glued to the center of the roof interior. I plan to outfit all my MTH R-Type cars with these LEDS.
Regards -- Joe F