The way Jamma is configured with Tekken 1-3 by default, only buttons 1&2 will work. However with Tekken Tag will have buttons 1,2 & 5 (Left Punch, Right Punch & TAG) Jamma I thought was 3 buttons by default. No? Which is why in SF only the 3 punches work. Weak, Strong & Fierce.
So with Tekken 2 it's just Left punch and Right punch. So yes you will need a namco 48 pin extended jamma kick harness to get buttons 3 & 4 (Left kick & Right Kick) to work.
If you look on your PCB there are two sets of Jamma teeth. One is for your Jamma harness, and the kick harness (Small section on right side) The wires are then run directly to your kick buttons.