My Mk2A is similar to yours on the front (led side) but on the back of yours there are another pair of elongated tracks where you have soldered your wires to. Are those connections not connected electrically to the whole back plane - i.e shorting the wires?
Maybe try just soldering the wires to the front (track side) of the board but drill out the through hole plating first
Maybe try just soldering the wires to the front (track side) of the board but drill out the through hole plating first