Sixaxis led mod obtained from PS3hax.net
Tools needed: small phillips screwdrivers, 15 watt soldering iron, small razor knife/xacto knife, tweezers or a hemostat
Supplies needed: one SMD led, fine rosin core solder, 30ga wire (kynar), double sided tape

Start by removing the five screws holding the controller together. To separate the two halves, gently pull the housing apart at the front/ usb plug side while applying pressure to the point where my thumb is located in order to release the catch:



With the bottom removed you can then take out the battery (pull on the plug, not the wires) and the reset button extension (circled in red):



Now remove the single screw holding the pcb and lift out the controller internals and shoulder buttons together:



Try and leave (or replace, if they came out) the D-pad and buttons in the top half of the controller shell. At this point you can remove the thumbsticks (they just pull off) and separate the flexible circuit board from the plastic carrige below it. It is anchored at the corners (circled):



With the flexible circuit board flipped out of the way, lift the plastic carrige off the pcb and undo the plug for the motion sensor (pull on the wires, this one's not as tight as the batttery) and then pull the flex. board out of its connector. At this point it wouldnt hurt to trim the tube on the plastic carrige (circled) back about 1mm to allow room for the led wires:



I had to borrow this shot from Senyx 'cuz I can't take a decent enough pic to show the detail (proving once again that if you make something idiot proof, like a digital camera, eventually someone comes up with a better idiot).
Anyhow, the picture is pretty self-explanitory as to where to solder the wires. The anode side of the led should go to the motion sensor plug and the cathode side (should be marked with a small black line/stripe) should be connected to either the 5 or 7 hole, as both are grounds. The led itself should be located over the "LED 5" solder points with double sided tape.



Reassembly is a straightforward reversal of the disassembly except that the L1/R1 buttons and the filler pieces between them and L2/R2 should be left out untill you have the pcb secured in place with its single screw. Once this is done, place the L1/R1 buttons in place (you may have to lift L2/R2 a little bit to do this) and then, while holding L2/R2 back with your thumb, slip the filler pieces back into place.



Once this is done, the battery, reset switch extension, and the bottom half of the shell can be replaced and you're done.

I will test this on my old pad, when the rumble pad comes out.