Using a Modbutton, Surefire DS00 tailcap, and 18350 body PLHV2. Light worked perfectly fine with the Surefire UE tailcap that I just sold to get the DS00, so I’m fairly confident that the DS00 is causing the issues. When I say that the light is really dim, I mean it might have like 5% of normal output. Dim enough that I have to stick my hand in front of the light head to tell whether the light is turning on when activating the Modbutton or DS00 clicky button. Even the the UE tailcap worked without issue, I still switched out the battery to a different known charged battery and still had the same issue. Can anyone tell me that’s going on? Is it a bad switch from Surefire? If so, will they warranty it? Will the next one I receive from Surefire have the same problems?

Is the light as dim when you use the switch on the ds00?

Do you have access to a multimeter to measure resistance between the spring and body of the switch? (preferably a bare metal part, not the finished surfaces) I'm assuming nothing happened to the modbutton, but might as well check the contacts on that cable too.