Crimping ferrules onto the wire ends was an improvement added to later production JuiceBoxes. You can add this layer of protection yourself by crimping ferrules to the wire ends before installing a new relay.

Strip a bit more insulation off the wire strand, to allow the wire to fill the full ferrule.

Insert the ferrule on the wire end, while stuffing the wire insulation into the plastic collar so that the copper strands are just poking up to the end of the crimp.

Insert ferrule (now with wire) into the crimper (but don't crimp the plastic collar!), and squeeze to crimp - these crimpers are self-adjusting to wire size.

Repeat for all 4 wires.