try this:
remove battery, tighten head, loosen, tighten, loosen, then tight again… a few times… my thought is to seat and get good contact of the inner and outer tubes, into the head
fwiw, the switch itself is a very simple affair… the issue is probably not the switch. I expect it is just poor contact from the inner tube end, to the pill.
if that tight twisting fails,
It might be poor contact at the tailcap instead.
one step at a time… the tailcap is glued shut because there is no retaining ring. If tailcap is removed, switch falls out.
btw, at 3.7v a battery is almost half empty. Youre not hurting anything by testing the light at that voltage, but I suggest you charge the batteries before any prolonged use.
Here is a photo of the tail, disassembled:
.
feel free to private message me if you like. I will be happy to help you figure out how to remove the tailcap, if it comes to that.
first, let us know if the twisting exercise solves the problem.