Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accruately.
This is not as bad a problem as people make it out to be. When you do your tune up just make sure the plugs are tight. Thats it, you dont need a torque wrench, you just need to tighten them up. Also, you dont need to replace all the coils, just the rubber boots. This is like replacing the plug wires. The od light not working is usually caused by a bad wire between the shifter handle and the steering column. Unfortunately you can't repair the wire. To repair you will need to replace the whole shifter assembly.
I hope this answer has been helpful to you! If you have any further questions please feel free to ask.
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Plugs, coil boots and labor will cost around $400 to $450 depending on area. Usually a good tech can get this done in 2 to 3 hours.