go_to_the_light said:
I did the trueblue mod on an L4 switch. It works as promised, but I barely get the tailcap on before the light turns on. Like I barely even start to screw it on. Not very usable. Should I shorten the spring?
Hmm, sounds like something is making contact before the ground plate of the switch. Maybe the resistor is touching the inside of the tube and allowing a path that doesn't go through the switch. Make sure there is adequate clearance so the resistor leads don't contact the tube at all. It's tight, but with an adequately small resistor (I've used 1/6 watt), it will clear.
Another possibility is that the anodizing has worn off the threads of the tailcap and are now conductive. If so, and if also the chrome ground plate of the switch is touching the tailcap housing, that is another path that is bypassing the switch. Make sure the ground plate of the switch is isolated from the tailcap, file the OD of the ground plate if necessary.
Shortening the spring will help, but it's not the problem. If for whatever reason you can't fix the cause of the problem, replacing the spring with an appropriate height solid slug will be a better connection and a better twisty action. But again, I'd highly recommend addressing the short instead of the spring.