Based on gunrunnerjohn's recommendation, I installed nGineering Mars light simulators in two American Models FP7s and two E8s. It had bothered me that the lighting effects on the stock models were not prototypical with a single incandescent bulb shining through the two headlight openings on the FP7s and an LED in the wrong, upper headlight position for the E8s. I replaced the incandescent bulbs with LEDs on the FP7s and re-positioned the original LED on the E8s to the proper lower headlight by trimming the body of a plastic ball-point pen and gluing it to the interior to hold the LED in place. I also toned down the bluish color of the original LED with a little clear orange paint.
Finding room in the locomotive bodies is no problem--the circuit boards for the simulators can fit in N gauge locomotives--and that poses its own difficulties. I learned that is it much easier to solder the tiny wires that come with the boards rather than attempt to solder the LED legs to the boards. On one board I inadvertently used a warm white LED from Richmond Controls that had a protective diode and capacitor, and this combination caused the light to strobe rather than increase/decay the way it was designed. Removing the protection got it to work properly.
The result is much more satisfying and interesting. Santa Fe operated its passenger E8s with Mars lights operating all the time. The Great Northern did not own FP7s, but I'm not going to point that out to anyone. The video below shows the modified locomotives running on DC with room lights dimmed a bit. If the locomotives were converted to DCC, the Mars effect and headlights could be turned on while they were standing still, but that's an expensive investment at this point.