Part of my bicycle-lighting project involved crimping a splitter cable to split the output of the dynamo to the front and rear lamps. I used a DuPont connector for that because I had recently bought, after 4 years of consideration, a proper DuPont crimper. The input and output wires were 24 AWG solid wires with an insulation diameter of about 1.3 mm.

A DuPont crimp actually consists of 2 crimps, one onto the stripped wire, and another onto the insulation for strain relief. The biggest challenge when attempting to crimp 2 wires is getting the insulation of both properly into the connector. The wires have the tendency to jam into each other; one wire doesn’t go in far enough to get its insulation properly crimped.

There are a number of ways to address this. In all cases you have to widen the insulation crimp tabs with some pliers. Then, you can either insert the wires into the connector and pre-crimp them with pliers; or insert them very carefully while the connector is in the crimper, judging the correct depth by how much the stripped ends stick out; or tape the wires together to ensure they don’t jam one another, and insert them while the connector is in the crimper. It doesn’t appear to affect to crimp strength whether the wires are stacked vertically or inserted side-by-side horizontally. Jamming is less of a problem when stacking vertically, but it is easier to judge crimp quality when the wires are side by side.

Crimping two wires actually has to be done in two steps, using both the medium and small crimping dies. The wires don’t fit in the small die; and the medium die doesn’t make a tight enough crimp to properly hold the wires and allow the connector to enter the housing. Before using the small die, it is necessary to pinch the sides of the insulation crimp together somewhat — if you don’t, the crimper tends to fold the crimp tabs around the sides rather than wrapping them around the wires.

In my case, the 2 wires did not fit into the connector housing without some persuasion. The insulation crimp did a fine job of compressing the insulation, but the uncrimped part of the wires that needed to enter the housing was too big. To fix this, either use pliers to squeeze the insulation into shape, or reverse the connector in the crimper, aligning the insulation part of the die with the insulation crimp, and the stripped part with the uncrimped wire to form it into shape.