First of all, you have to be very careful where exactly you click, as hotspot placement in this game isn't the best. :-[ So try to make sure that the upper left corner of the standard four cursors is on the exact spot you want to click on, and the very middle of the inventory tools cursors is on the spot.
Hint 1:
Spoiler
Try looking at the other three prominent wires and pay attention to what Abbrekt says.
Hint 2:
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You need a length of wire to fill in the gap of the yellow wire.
Solution:
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Use the file cutters on the green wire. Then use the soldering icon on the yellow wire. You have to click on the wire itself, not the gap.
Hope this helps.