2002 ford f150 4.2l wiring diagram

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Firing order for ford engines is shown in the attached link
Firing Orders for Ford Engines

if it's a four cyl engine then it's the first plug on the passenger side of the car.

i am suggesting you a link from where you will get the the diagrame http://toolsnyou.com/

what size engine do you have 4cyl, 6cyl, this will affect which diagram i am able to supply to you to correctly help

Below is a picture that should help.

Hi :) Here is the 2002 Ford Mustang GT wiring diagrams for sparkplug wires.
4.6 liter SOHC V-8 VIN "X"

here is a diagram, if u can't see it go to the link below.
http://autorepair.about.com/library/firing_orders/bl-fo-9225.htm

To change a spark plug. 1.Disconnect the wire attached to the spark plug it would be wise to do only one at a time! 2.Take a long socket that will fit the spark plug 3.Attach to the socket wrench and turn counter clockwise until off. 4. Put the new spark plug in and hand screw until tight then turn the socket wrench clockwise until completely tight usually 1 1/2 turns. 5.Then reconnect the spark plug wire. Easy as that. Repeat steps 3-5 for the rest and remember ONE PLUG WIRE AT A TIME!

here