2004 f150 have to replace engine wiring harness. Have a used harness but can’t find a shop to install. Can I install the harness myself? Not a mechanic but relatively capable

 

Just two questions. What makes you think you need a new harness and is the old harness still in the truck?

 

Long story. Lost AC, temp gauge pegged low, CEL. Told CHT sensor bad. Replaced but did not solve problem. Mechanic replaced pigtail from CHT to harness now truck starts won’t run. Took to another garage they told me the harness had been cut and taped up previously. Nobody wants to touch it. The old harness is still in the truck and I found a used one. They told me it would be too expensive to trace all the circuits. Just trying to save my truck.

 

I don’t see why you couldn’t pull this off.

Lay out the replacement harness over the engine and start swapping plugs into connectors.

Hopefully, someone chimes in with a schematic out of a factory service manual to get you an idea where each end goes. The plug ends are almost all unique to the sensor/etc they connect to, so it’s not too likely you’ll get them mixed up.

 

Thanks

 

Have you made any progress? I just had the engine harness out of my 08 4.6l and it was not bad at all. I'm sure the harness between the 5.4 and 4.6 is fairly similar. For the 4.6l, If you think of the harness as a "U" shape, the end on the driver side starts down near the oil filter where it plugs into the rack and oil sending unit. Once those two are unplugged you can come up to the corner of the valve cover and undo the tab that holds the harness in place. Then you undo the knock sensor, cam sensor (probably a phaser sensor on 5.4), stereo transistor, and start unplugging the injectors and coils. Half way down the driver side you will most likely unplug your EGR valve. Then at the back corner on driver your O2 sensor goes down and you'll have to pop under and unplug it. Then you go over to the passenger side underneath and undo the O2 sensor, this was the hardest for me. Then start coming from the back to front undoing coils and injectors. Halfway down the passenger I had to undo the fuel pressure regulator valve and heated PCV. At the front passenger corner there is another stereo transistor and cam sensor. Then you'll go underneath again where the crank sensor and A/C compressor plugs in and undo those. Once you have those out you can undo the connector at the PCM and the jump over connector right under and slowly feed the harness out. I may have missed a sensor here or there but that should be the majority of it, atleast for an 08 4.6l 2v. Also, right by the PCM there will be a tag with a part number. Make sure your harness youre installing has the same number because those harnesses change ALOT.

 

I have another mec. Looking at it. I should know this week if I really need to replace harness. I had.the replacement checked by Ford using vin # and it’s the same part number