looking to install a aftermarket tach in my 2002 f150 4wd 5spd, what i am curious on is behind the instrument cluster which wire running into there would be the tach lead wire if you had a factory tach, i know in my old ranger i was able to tap in pretty easy there just cant find a answer in my haynes book or anywhere online, hoping someone on here might have some info, thanks in advance

 

Your motor has 8 coils over the plugs.
The Tach signal to the dash is not usable by a standard Tach because the signal does not represent the time interval and wave shape the meter needs to see.
The electronic dash has it's own Micro Processor and translates complex signal for tach and speedo readout.
If you have the electronic dash, there is a way to see RPM and other funtions read out on the mileage digital so you can do a compair.
Go to the AUTOMETER website and see the adapter #9117.
This adapter requires you to find the 12 volt feed to 'all' the coils 'only' and install the adaper inline per instructions.
What that means is the power through the fuse feeds coils and fuel injectors plus some other items so you will isolate just the coil feed.
What you have then is a pulse everytime any coil is fired same as the old style single coil would offer for 8 cylinder or any number of cylinders.
The after market tach should count these pulses through the adaper the same as it would in an old motor application when the Tach is set for 8 cylinders.
The after market Tach is a time constant function so averages the time and frequency of the signals it receives to drive the meter according to the cylinder switch setting..
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If you do it any other way, you will/can have large accuracy issues.
The stock signal is subject to the gear ratio and tire size programming in the computer Ident block and word layout.
This adapter only looks at the engine RPM represented by the current flow each time a coil is grounded by it's solid state switch in the computer.
It works much the same way as a 'pickup clamp' on a good timeing light.
I can look at the timing advance on these motors by using a timing light clamped around cylinder #1 coil or fuel ijector cable and looking at the factory reference down in the crank pully area.
If the light is a dial back type, you can tell about the actual advance you see.
Otherwise I can see it full time on an aftermarket dash monitor along with RPM, temps and many other outputs I can select for any 4 visuals at a time..
Good luck.