40-Way Female IDC connector, 0.1" (2.54mm) pitch

This IDC (Insulation Displacement Contact) connetor press-fits onto 1.27mm pitch ribbon cable.

The main body of the connector is 2 parts, already pre-assembled. Simply insert the ribbon cable and press down. Note that one side is marked with a small arrow, this is traditionally for pin 1 / conductor 1 (usually marked in red or blue color on the ribbon cable). It does not matter from which side you enter the ribbon cable into the connector, as long as you align the color-marked conductor with that litte arrow. The marker is on the side with the "bump"

After crimping down, rightly fold the ribbon cable over the top and install the strain relief brace. This should snap in place without any significant pressure, just "by hand"

Important Tips

Use a crimping tool to make the crimp, or a vice. Do not use pliers, because you really need to apply even pressure along the entire width of the connector, all at the same time. Do not try to "piece-meal" crimp
Ensure that the cut on the ribbon cable is at exactly 90 degree, and straight. Knipex has a hand-tool for making straight 90-degree cuts.
Make sure the ribbon is inserting the connector at an exact 90 degree angle.
Do not exert too much pressure when crimping

If you don't follow the above instructions, you may end up with a crimp that looks OK but you end up with shorts between neighboring conductors in the ribbon. The most likely culprit is too much pressure during the crimp operation.

Finally: The connector has a polarization bump, so it fits into a shrouded / box header only one way. Be aware that the cable gets folded over the connector before adding the strain relief, so the cable-entry and bump location are "inverted" from when the connector is crimped vis-a-vis when the strain relief is mounted.