I have a 1999 Nissan Frontier where do i hook a aftermarket tach _ wire cant find a place on my distributor please help

Try any noncommon wire on any of the injectors. For example, if you have 4 injectors with two wires each, and there is a common blue wire on each injector, it's not going to be that one. You'll notice that the other wires are all different colors. These will work as a tach signal. These are read in AC voltage and vary from 1-7 volts AC. Before you go splicing into it, get a cheap digital Voltage meter from Radio shack or a hardware store. Ground the black cable from the meter on the vehicle and stick the red cable on a non common wire and move the throttle blade back and forth. If the voltage goes up and down while on AC, you have your tach signal.