Bikonja:
So I haven't been replying because the discussion was ongoing and it was mostly just greek to me.
Did you examine the melted connector of the jumper wire to see if the construction was bad or some threads in it where broken? The usual dupont wire (AWG28) is only good for ~1.4 amps as a GND (chassis) wire. If some threads in the wire are broken or not properly connected this value will decrease.