Here's the instructions for install on the new switch. I've never done one on the old switch.
First, remove the brass screw in the side of the round metal bulb holder and it will come out. Also remove the large spring with the metal caps on both ends. Then pull the hex nut with the setscrew off the end of the blue part of the switch and pull the long metal strip it is attached to out of the bulb post. You may also want to remove the center switch portion completely to keep it clean while you cut down the switch. It just pushes out the button side of the switch body. You should now be left with just the main part of the switch body with only the little metal cup and spring that contactxs the end of the battery still attached.
Now as for where to cut. There is the large diameter area where the actual switch was and the smaller diameter bulb post with four small braces at the bottom. You want your cut to be at the bottom of the bulb post where it attaches to the larger switch body. You need to remove the entire smaller diameter bulb post and the four braces. What I usually do is use some pliers to just snap off the four braces first so I have a smoother round post to cut. Then I cut off the bulb post, but I leave about 1/16-1/8" of the post sticking out. Then I sand down the remainder to give me a nice flat smooth end on the larger diameter switch body. The reason I do it this way is to help with centering the metal portion of the Kiu kit. You'll notice a small lip where the switch body sits against the retaining ring inside the barrel. This works well at holding the metal part of the Kiu kit centered while drilling and mounting. When I tried to cut the bulb post off flush in one step, I often cut into the top of the main body and removed this lip by accident.
Once you have the post removed, put the metal base of the Kiu kit on top of the switch body. I like to line the screw holes up with edges of the vertical side portion of the switch body. This makes sure the screws will not interfere with the center switch portion. I use a 3/32" drill bit to drill the screw holes. Then I remove the metal base and drive the long screws from the kit into the holes to form the threads in the plastic. Make sure you keep the screw square to the hole as you do this to make a good set of threads. I also use a chisel to knock out the little plastic divider seperating the round hole and the slot in the top of the switch body. It makes the next part, the wiring, easier.
On to the wiring. First install the metal base on the switch body with the screws, but do not install the posts for the ceramic socket yet. Then insert the wires for the socket throught the center hole of the metal base and fish one wire out each side of the large switch hole. Now you need to cut the wires to length. I try to keep them as short as possible, but it's better to leave a little extra if you are not sure. It's possible to coil up some extra wire under the metal base when you're done. I've done dozens of these so I cut them pretty short. The wire coming out the round button side of the hole I cut about 1/4" past the outside of the body, just enough to let me strip the insulation from the wire and solder the positive contact to it. The other wire on the "squared off" or oval side ot the switch hole I cut to about 5/8". The extra length is needed to reach the ground screw. You can wait to do this ground wire until after you solder and position the postive contact wire if you want to be sure of the length. It will still be accessible, the positive wire won't be.
Solder the positive wire to the metal contact on the side of the blue switch body. If you are good at soldering, you can do this with the metal still in the plastic body. but if you tend to overheat parts while soldering, pull the switch apart slightly to remove the metal contact for soldering so you don't melt the plastic and then reinsert it when you are done. For the ground wire, you need to cut the long part of the metal strip off the ground screw. Again, depending on your soldering skills, you can either cut it flush at the bend or leave a little extra length to make a little tab that is easier to solder to. But don't leave the tab so long that it sticks up high enough to contact the metal Kiu base. Solder the ground wire to this tab.
Now for the final assembly. As you insert the blue switch into the body, pull up on the ceramic socket to keep the wires straight. You may find it easier if you unscrew the metal base and pull up on everything at once. If you've left your wires extra long, you'll definitely need to do this to tuck away the extra length. Once you have the switch full inserted into the body, you can fit the ground screw on the other end of the switch. You should now have the ceramic socket sticking above the metal base enough to allow installation of the support posts. If you keep the wires short, you just need to push the socket to the side, screw in the hex standoff posts, then move the socket back over the posts and fasten with the short screws. If the wires are a little long, you want to unscrew the metal base from the plastic body, attach the ceramic socket to the metal base, and then reattach the finished assembly to the plastic body. If you gently twist the metal base as you are installing it, you should be able to coil up any extra wire so it fits in the small gap under the metal base. Fasten it back down with the long screws.
A couple final notes. You will need to remove the snap ring from inside the body to allow for the length added to the switch by the Kiu kit. I find the easiest method is to use a smallish flat bladed screwdriver. Working from the head end, put the tip of the screwdriver at an angle so that one corner is under the lip of the snap ring. Then give the screwdriver a little twist to lift the end of the ring out of the groove while pushing down on it at the same time. Once you have the end of the ring started, just work your way around the ring by pushing down and when you're about halfway around it will usually pop out of the groove and fall out the bottom of the barrel. Fianally if you have difficulty inserting the finished switch, there is an easy solution. Sometimes the metal part of the switch shifts on the plastic part and makes it hard to put in. If that happens, just loosen the screws a little to move the metal and plastic parts of the switch back in alignment and it will slide in and you can retighten the screws.
