Hey guys! I need a bit of help with the right steps to wire my logictech mouse... which I modified. (removed buttons , re-soldered new pins and attached wire) However... there are 3 pins for each button, and 3 buttons in total as you can see from the picture. The extra button is under the LEFT click. My SPST momentary switch has 4 pins sticking out of it... I'm slightly confused as how to wire the "three wires" to this button. Seeing as the wires are probably, positive, negative and ground. However I don't know the order of the positive/negative on the switch... or on the mouse :(. Ground can be shared but once again I'm not sure how to go about this.
Please help... I'm new at this. Thank youuu!
The 'microswitch' style button switches in the mouse are probably double-throw, One pin is common, one is normally closed (NC) and one is normally open (NO). Probably uses the Normaly Open side and leaves the NC terminal unconnected (check the circuit board).
The NO button you have has two pairs of pins. The switch connects one pin to another. Having four pins has several advantages including making for a more stable support when soldered onto a board and doubling as two jumpers which may make it possible to use a single-sided board without additional jumpers.
Hope that helps. Let me know if I can help with anything\ else.
thank you very much 
that's very informative.
mainly at the moment... i'm simply trying to figure out which wires to solder to the switch..this might sound like a dumb question but.. i soldered 2 out of the 3 wires to the button. if i plug it into my usb will i short circuit anything or mess up my laptop? probably not since the power is very low. just to test it out.
Nevermind.. I tried. Luckily nothing happened. Button doesn't work. I'll go out tomorrow and buy another mouse model... hopefully it will have two pins to make this mouse hack easier.
I'll go out tomorrow and buy another mouse model.
You'd be a lot better off buying a multi-meter, instead. Quit guessing. Know.
You can use a battery and light to check the switches you removed to see which two pins are the NO switch. Then figure out which holes in the PCB those were in and solder to them.
Another way: Look at the copper traces on the bottom of the mouse circuit board. Usually all three switches will have one pin connected to Ground (all connecting to the same long winding trace) and one connected to the chip (fairly short trace from the switch to a chip pin) and one pin not connected at all. The two pins connected to traces are the ones to use. Test it by plugging in the mouse and connecting those two pins by touching the two ends of a wire to them. If they do what you want, that's where you connect your button.