Solder connections carefully. make sure all points have contacts where there supposed to have them, you should also be sure to think out how its going to be put together. for example when i put mine together i realized that i had to put the lights on one end of the flashlight casing then feed the cables through and solder the other end on at the other side. Also be sure to solder the LED's in their proper direction or they will not work. another thing i did was use the existing switch on the flashlight and separated the ground by it, so that i could control its on/off function with it.