I'm sorry to say, but you get what you pay for. I don't think I'll ever buy a solar-force product again.
That's fine. More for the rest of us. But I believe the OP was asking for help, not your thoughts on the brand.
To the OP...what recDNA said is right on. Try to isolate the problem and then take care of it.
I have an S5 tail cap that was had issues when I first got it. Turns out that the retaining ring inside was loose just as recDNA mentioned. Tightened it up and worked fine. I think I've taken the light apart lego-ing it more than I have used it. Took the extension off of it last night and it wouldn't turn on and when I got it to, it was dim and flickered. The retaining ring worked loose again. Tightened back up and works flawlessly. I don't know that I got it sufficiently tight the first time cause I didn't have the right tool for the job.
Let us know what you find out.
Edit: In the process of typing this up, a bunch of people replied. So take my advice with a grain of salt (and a lime and shot of tequila, if needed!) :nana: