the plug coming form the distributor... the 8 pin plug. there will be a blue wire on the distributor side of the plugs and nothing on the other side, that's your tach wire. The 99-00 EX models don't have the tach wire run to the shock towers, the tach signal comes from the ECU.

personally if you're putting the tach on/in your dash... I'd hook all the wires up behind the cluster. Power, ground and tach signal are all right there. no long wires to run.
tach - solid blue
power - solid yellow
ground - solid black