The best way to insert the cable into the RJ-45 connector is this:
Hold an RJ-45 connector so that the plastic release clip is facing away from you, and the opening for the wires is pointing down.
While squeezing the cable so that the jacket does not move on the wires, insert the sorted and aligned wires carefully into the RJ-45 connector partway. You’ll feel some resistance as the wires enter the grooves in the connector.
Looking at the side of the connector that’s facing you (should be the one without the clip), verify that the wires are still in the correct order. Sometimes the act of pushing the wires into the connector can cause the order of the wires to be switched at the last moment. Use a magnifying glass if needed.
Push the wires the remaining way into the connector. Make sure that the wires have gone all the way into the connector and are touching the end of the RJ-45 connector. You should see a line of 8 bare wire ends. If one is missing and that individual wire hasn’t gone far enough into the connector, pull the wires out, line up the ends and put them in again. You can’t see this problem from the side – you can only see it from the end.
Now push the jacket as far as it will go into the connector.
Getting all of the wires lined up and inserted correctly can be a little tricky, so take your time. This gets easier as you get the feel of it.
If everything went well, it should look like this:
See how the end of the insulation sits snug inside the RJ-45, and how the wires go all the way to the end?
Below are two examples how it should NOT look. In the example on the left the wires were left too long, which leaves wires unprotected between the RJ-45 and the insulation. In the example on the right, the wires were cut too short and now don’t reach far enough to make contact.
Double-check one last time that the wires are aligned correctly and all the way in. Then insert the RJ-45 connector into the appropriate opening of the crimping tool. Give the handle a nice, tight squeeze without crushing the RJ-45. If you have purchased a pair of ratchet type crimpers you will know that you are done when they release. If you bought a cheap-o pair, check to make sure that all of the little metal contacts are even and at the same height below the plastic of the plug.
Now repeat this entire procedure to put an RJ-45 plug on the other end of the cable. Use the exact same wiring scheme as on the first end, which will make it a straight-through cable.
Note: If you decided to spend a couple extra bucks on the strain relief sleeves, be sure to put them on and facing the correct direction before you crimp the second end.