I just put in the proper p72 obd1 ecu and my tach doesnt work. We are unsure why since this is not a common thing to happen with swaps. The engine runs fine, and runs quite well I might add...but no tach. We can rewire it, but does anyone have any suggestions? I have looked at wiring around the net after searching, but nothing we can find is related to a tach issue. The car is a 94 Si hatch, and the engine is an obd2 w/obd1 p72. obd2 engine harness, obd2 distributor . . . No codes are thrown, I just have no tach! There is an extra plug that was not used from the obd2 engine harness, it contains 3 wires and is located next to the passenger side harness plugs into the firewall.. I know the middle wire is for the Knock Sensor, and what are the other 2? Searching has not helped..