The quotes around the word real are there because this idea acts like real Rule 17. But since we don't have 3 position rotary switches on our throttles, it's not quite the same.
Here's how it works on the throttle (after you've done the hard part--the work):
If you have a locomotive headed out on the road with a train, assuming your headlights are off, push the Headlight button and F7. The headlight on the front of the engine will come on. The lights on the rear will stay off. Take your train out. If you feel the need to dim your headlight, press Headlight. When you want it bright again, press Headlight. With this setup, you will be toggling back and forth between bright and dim. That is exactly what you would be doing in real life.
Thus you can dim a bright headlight at will with this system. And the lights at the other end of the loco will stay dark. Because they are on different buttons, and have not been turned on.
If you reverse the direction of this train, the lights will stay as you have left them. That is, if you have a bright headlight, and you back up the train, the headlight will stay bright. And the lights on the other end of the loco will stay dark.
Should you wish to run around the train and pull it back to the yard, you will press Headlight to dim, and press F7 to off. The front headlights will then be off. Then press F8 and F9. You'll then have a bright headlight on the other end of the loco. Which can be dimmed at will.
Now let's say you want to use that same loco to switch the yard. Assuming the lights are off, you hit F7 and F9. The lights at each end of the unit will be dim, presuming that's what the yardmaster wants in his yard. And they will stay that way until you decide they should be different. Direction of travel will have no effect.
The simple explanation of this system is that you have two functions feeding the front lights (activated by Headlight and F7), and two functions feeding the rear (activated by F8 and F9). Headlight and F8 are set to full bright. F7 and F9 are dimmed. The manner in which these buttoms are pressed determines what the light outputs are.
There are, of course, the details. For one, you will have to use a 6 function decoder with appropriate dimming. This will give you ONE extra output for auxiliary lighting, like roof flashers. The TCS A6X does this beautifully, if you don't want sound. There are also 6 function sound decoders. If you need more outputs, I expect someone will make such a decoder, if they haven't already.
You will also have to do some wiring and some CV inputs. I just did it to try things out.
It worked GREAT.
Ed
Thanks, Ed
I'm copying your "dissertation" for future use. I have a bad habit of installing a decoder, then programming the bare minimum CVs with the assumption that I'll get around to "fine tuning" at a later date. I'm 62, the layout is 22 and I've been running DCC for 12 years. Maybe that "later date" is here
Regards, Ed II