Perfect, that’s what I needed.
Try this:
GITD Tailcap + UV LED
The Tailcap will be enlightened from the inside…
If I understand this correct: All I need is one of the boards, the switch, a resistor and a LED - nothing special like a cable running from one end of the light to the other or a special driver or something like that?
You don’t need to run a cable or a special driver. You will need to add a resistor to whatever driver you are using though. I have it working with 3 different driver designs, but I suppose there is still the potential that a driver may not function with this mod installed.
Can you link where this action is described for dummies? 
Edit:
So, just adding a resistor between plus and minus of the driver/battery - correct?
So minus becomes plus for the LED through the resistor and the electrons can float…
Just ordered a few of the 17 and 20mm ones… can’t believe how cheap OSHpark is…
My first order from them btw 
Correct. I just solder a dip resistor between the batt+ driver spring and the driver GND ring. I’ll post a pic of one of mine later. Its super easy.
pilotdog 68 very interesting stuff you have done here. I’m curious if you have any info on how much battery life do these leds in the tail consume?
Yep. It’s in the top of the OP. It’s around 0.2ma.
I have finally seen the light this is a really great idea.
I don’t know why it didn’t interested me before, but then i thought about that a low moon mode with a white lead still has lots of blue & green that can effect melatonin production & make the eyes lose its dark adaption & that we can buy cheap ebay red & amber ledstrips to harvest leds from to build red & amber glowing tailcaps instead.
Proper moon mode really should have red or amber, and without a moon mode in the firmware we can always start in a usable for daylight mode & simplify the UI
Do you think it is possible to connect it to the switch? so that when the switch is off the tailcap light is on but off when the switch is on.
But maybe only complicates things more than necessary for something that pulls so little current.
But then when the switch is ‘on’ so is your main light. I’m sure something could be done though.
Currently I use it on lights that have tail-cap lockout, which shuts off the tail LED’s when I don’t need them.
I also ordered some tiny switches to see if I could fit in a way to disable the tail light for storage, but it would be mounted on the inside next to the battery spring. I’m still working on that.
A switch for the led in the switch? I love it. Dip switch maybe?
Maybe.
i was hoping to find smaller, but I ordered some of these. Now I’m just waiting on delivery to see if it’s feasible.
Interesting. How do you intend to place them or se those switches?
It would be something to disable the tail when the light isn’t in use. If I can get it to fit, it would be on the inside of the light, next to (or even inside) the batt- spring. You would have to take off the tailcap and use your finger or pencil or something to flip the switch. It would only affect the tail led’s, the regular light would function normally.
I’m not completely sure it will work at all, and wouldn’t really serve any purpose if the flashlight has tailcap lockout anyways.
looking pretty cool any updates on the build?
Umm not really.
I have it installed in the 2 lights I use most, the red and blue ones from the OP. Works Great.
Once oshpark delivers my new PCB’s I’ll play around with adding diodes for a pseudo-LVP.
I’m kinda surprised nobody else has done it yet. I know a few other people are waiting on Oshpark as well.
If someone in the US wants some of the clear switch boots, I have a couple extra I can send, either 14mm or 16mm.
I haven’t read all the posts in both threads so this could has been suggested before.
But a way to detect battery level would be very cool to get in the tailcap but maybe it is not possible without a connection to the positive terminal.
I think that’s a great idea.
Awesome, I need to build one or two of these.
Thanks for putting together a great idea. I just ordered some boards and components, enough make a couple dozen. Now for the long wait for everything to show up.
Big thumbs up.