Troubleshooting a bad high mode?

I'm in the process of building my first flashlight from scratch. I'm a tolerable (hah!) machinist, but I'd still consider myself a novice when it comes to electronics.

Everything is ok so far, but I'm having trouble with the high mode functioning correctly. The low and medium modes work great, but when I click through to the high mode only it flashes on for a second and then stays off. I'll try to include as much detail as I can, but if I've missed something important please say so. While I'd like to get this particular problem figured out, general troubleshooting advice is very much appreciated. My two ideas right now are 1) I've damaged the driver while I was soldering it to the pill or 2) There is a loose connection somewhere in the body of the flashlight.

I'm using the following:

Nanjg 105c (http://www.fasttech.com/products/1699/1122302) jumped to the 3rd star for just three modes.
Cree XM-L2 T6-1C (http://www.fasttech.com/products/1699/1277804)
18650 li-ion battery (nuon brand, whatever I could find locally, it's fully charged)
McClicky switch

Any ideas?

Test your battery - First bare, then through the power contacts of your driver. Select a high-power resistor (Or one you dislike) and an appropriate fuse (1Amp, 3Amp, something reasonably low) and test that the battery can deliver current, and then that it can deliver current to the driver. Test your switch - Connect the driver, LED+Heatsink to the battery, and manually make/break contact. If it works now, something is wrong in the tailcap - retaining ring loose, Clicky damaged, threads not making electrical contact, or spring are most likely. Test voltage - Vinput at the driver, in low, medium, and high. If the battery "turns off" (Under 1v) on high, then you are tripping out an electrical safety somewhere. If the battery voltage falls to 2.x volts, you've got a pitiful cell.

AnAppleSnail said:

Test your battery - First bare, then through the power contacts of your driver. Select a high-power resistor (Or one you dislike) and an appropriate fuse (1Amp, 3Amp, something reasonably low) and test that the battery can deliver current, and then that it can deliver current to the driver. Test your switch - Connect the driver, LED+Heatsink to the battery, and manually make/break contact. If it works now, something is wrong in the tailcap - retaining ring loose, Clicky damaged, threads not making electrical contact, or spring are most likely. Test voltage - Vinput at the driver, in low, medium, and high. If the battery "turns off" (Under 1v) on high, then you are tripping out an electrical safety somewhere. If the battery voltage falls to 2.x volts, you've got a pitiful cell.

Click to expand...

That was exactly what I was looking for. Thanks!

Take notes on what you find. If that doesn't work, bring your notes and we'll go further. Best regards,