X600 Pins 3 and 4 are connected internally to Pins 1 and 2 respectively and are used for ease of cascading input signal to other panels. So the pair of wires go in on (1, 2) and leave on (3, 4). If the PAD-5-MB is the end, then the EOL goes on (3, 4). If not, continue the run from (3, 4) to the next PAD-5-MB (1, 2).