Well, bad news on the LED addition to my searchlight car. The CL6 constant current chip doesn't like something about the way I'm using it, and after some usage it partially fails such that it is still passing current to the LED, but it doesn't regulate it. The current becomes somewhat proportional to the input voltage, and at 18v, it's passing 200+ milliamps. Not unexpectedly the CL6 get *really* hot, and the 100ma LED eventually burns out.
I originally bought two CL6s, and both have suffered the same fate. For the second one, I used a pretty decent heat sink (complete with heat conductive paste) thinking the problem might have been heat related, but that didn't help. The second one failed the same way as the first one.
I'm guessing that the problem is the rectified but unfiltered input voltage. The CL6 is designed for DC input, and perhaps it doesn't like chasing the sine-wave like input voltage. Or it doesn't like the extra noise from the pickup roller when rolling down the track, with occasionally interruptions on turnouts.
The next time I place a Mouser order, maybe I'll get a couple more CL6s and try a capacitor on the input side to smooth out the input voltage. In the meantime, I'll probably have to just go back to some resistors that I can get locally.
I run mostly with TMCC so usually have constant track voltage.
