The firing pin safety consists of three parts. The assembled unit should look like this. In this picture the mechanism is is upside down, compared to how it will sit in the gun. (It’s probably not worth it to take it out unless it’s broken. To take it out, simply use a flat screwdriver and lift it from the opposite side of the slide.)
This is probably the trickiest part of the entire gun. Insert the 3 parts as one, with the pin going downwards into the hole it should sit in. The spring will need to be lifted across the slide rail, and fit a groove below. The other end of the spring should grip around the lower part of the safety, as in the picture.
The upper consists of a lot of parts that all jump in all
directions when you slide the back plate off.
The extractor will often not fall off, but is in fact completely free to fall. The same goes for the extractor spring rod, that will often sit stuck inside the tunnel where it is located. To fit the extractor onto the slide, put it in from the outside of the gun. It will have a very specific way to fit, and it will take some practive. You will know when it’s right because it will sort of lock into place. If you do not find the right spot you will know as soon as you plug in the spring parts.
Assemble the springs etc. in all 3 main parts, and put them into the holes in the frame. They all have different diameters, so you can’t put things in the wrong place.
The firing pin needs go in together with the firing pin spring parts. The firing pin has a little notch that should fit into the firing pin spring rod.
Put the back plate on, and slide it towards the two springs.
First push down the extractor spring plug, which will be the hardest to
push down. Use a tool that will fit the little hole in the top, to make
sure it does not slip. Otherwise it will do it’s best to escape and
make you look for it. As soon as the back plate is in position to hold
it down, you can let go, and then push down the firing pin spring
holder. This one is easy. Push the back plate completely into place.
Disassembly: Be careful here. The two springs will jump pretty far if you don’t catch them. Press down on the “round metal thing” you see on the back plate. It’s really the extractor spring, which also holds the back plate in place. Push it down below the back plate, and move the plate down.