First post, new to light building, I’m thinking of using a Kaidomain H17A driver (http://kaidomain.com/S028482-H17A-17mm-3V-4_2V-5A-1-cell-5-Mode-Driver-Circuit-Board) but I can’t find any instructions or a datasheet for it. Does anyone know how it should be connected up and how to change the modes? Does it need a push button?
The documentation is not very thorough for these drivers. I think the only documentation is that page.
From experience with other similar drivers I can tell you a bit about it. When installed in the flashlight the spring makes contact with the positive end of the battery. The battery negative makes contact (through the flashlight body and a switch) to the conducting ring at the outside perimeter of the driver, called the ground ring. It does need what’s called a clicky switch which disconnects the battery negative from the ground ring when pressed. Most of these switches are reverse clicky which means when the light is on a light tap on the switch momentarily turns the light off. This action changes modes in the driver.Most all lights with the switch at the tail have this sort of switch.
The wires on the other side are connected to the LED. Red to positive.
The H17A is a linear driver delivering up to 5 A to the led emitter in its standard configuration. The driver is primarily designed to work with reverse clicky switches, a switch type which engages when the button is released. When installed in a flashlight or lighting device with reverse clicky switch, you turn it on by pressing and then releasing the button. Once the button is released the light turns on. To change modes, the power button is slightly pressed (half-press, without clicking) and then released, this is something which cuts power to the driver for a brief instant.
The two wires onboard go to the emitter(s), while input power is positive at the center circle, where the spring is, and negative input goes to the outer ring (be it back or front side, makes no difference).
The thread KD (kaidomain): Deals and new products thread is a good place to ask about the driver. BanL, Kaidomain's manager, answer questions there.
Thanks guys, that’s really helpful, I’ll give it a go.
Guys, If anyone has some experience with these drivers - I have a bit of problem with one:
I replaced wires for a bit thicker gauge, soldering was done ok, no issues afterwards. Tried one led, tried another, finally when I was decided on which one to use, I soldered on the spring, then a wire inside it, and suddenly, the driver works in one mode only (around 30-40 mA), plus hidden strobe. It’s supposed to work 4 modes plus double click strobe. And it did, before the spring 
If anyone has any idea what I could have screwed up, throw me some ideas please. I don’t have microscope to post any useful pictures, what I can see with my naked eye, everything looks fine.
Were you testing it the same way? Like were you using a switch or just making contact with the wires by hand? I know when I am testing a driver just making contact with wires to simulate a tail switch I get some seemingly weird behavior because sometimes the wires are making contact several times, simulating many button pushes quickly, when I think I’m only making one contact.
Other than that I can only think if you accidentally changed something on the board when you heated it up to do the spring. Have you tried taking the spring off again and retesting?