Thought I'd share my recent milestone and success using a Gen 2 Coyote, PCM and wire harness from a 2017 GT. I purchased a wrecked GT with 17K miles and kept the engine, transmission, PCM and engine bay harnesses to put into my MKIV complete kit. The intent was to not use a control pack since I essentially had everything required to create a harness that would run the engine. Sold everything else from the donor GT.
I had read previous posts to use a donor harness with some successful and some not, so I was somewhat tentative about doing this myself, but I had previous experience and frankly, enjoy the challenge of going through the harness and diagrams to figure it out. This past weekend I successfully started and ran the engine on the first attempt. (Technically it was the second attempt due to a wrong pinned inertia switch connector on the Ron Francis wiring harness that prevented the fuel pump from functioning
- already posted about this). See video below of the first start - yes, I was pumped when it fired up.
I'll do my best to layout what I did and how I did it below.
Step 1: Isolate the Needed Harnesses
I use the engine harness, engine bay/PCM harness and the harness that is connected to the transmission, lower O2 sensors, etc.
Engine Harness: This one is easy. There are two connectors - 1) Large one that connects to the PCM and 2) smaller one that connects closer to the main fuse box. This one stays with the engine. Pretty sure it is the same as was what you get with a crate engine.
PCM Harness: This one is big, goes everywhere in the engine bay, and connects through the firewall on both the passenger and driver side. This essentially becomes the main harness similar to what you would find in a control pack. This has the main fuse box and has the main positive battery connections for the starter, alternator and electric power steering.
Transmission/O2 Harness: This one is small. Has a connector on the back side of the engine. It also connects to the starter.
Isolating the harnesses is not difficult nor technical, but does take time since there are many, many connectors and grounds. I'd recommend not tackling the PCM harness until the engine and transmission are removed. Then its all open and easy to get to. Removing the tape, loom protectors and such takes some time as well.
There are many other harnesses on a GT, but anything beyond the firewall is not needed. A key module to the GT, but is not used in this application, is the Body Control Module (BCM). Since the BCM routes/controls ignition, start, fuel pump, the DLC and other things accommodations must be made. This will also be outlined below.
Step 2: Strip Down the Harnesses
Engine harness: Do not touch. Good as is
Trans/O2 Harness: Keep mostly original. I cut out the lower O2 sensors. I am using the Speedhut gauges with GPS so I don't need the speedo output. I am still considering using a back up light so keeping the reverse switch would be helpful.
PCM Harness: This is where all the work is. The end result will use about 1/4 of the wires and about 1/5 of the fuses. Find an open place or use a good size table to work on the harness. Or if you have a spare wall available then you can hang it at working level which is what I would recommend. I posted pics below of the before and after of the PCM harness.
The main work here is to determine what to keep. This was a huge question when I first started since I was still working through what was needed to get the engine to run. I ended up having to re-connect some wires that I had cut earlier. Hopefully, this documentation will help others avoid cutting needed wires. I have outlined below what is required. Many of the wires I cut out were those going through the firewall to either the BCM (passenger side) or the driver side stuff.
In the after picture you can see what is needed. This is probably the best way to share what is needed.
Step 3: Customize/Modify/Add to the Harnesses
I only customized the PCM harness (other than trimming the trans/O2 harness) in order to run the engine, add some circuits (FB vents, seat heaters, cubby power etc) and utilize some features of the existing harness. Many circuits/connectors did not need modification (accelerator, alternator, engine) others needs some added to or taken away. Fuel pump uses the Ron Francis body harness, but needs to be tied into the donor fuse box. I may still try and use the PCM to control the fuel pump. I am using the fan wiring as well, but only need to connect to one wire and the ground instead of all four.
The large gauge wires from the donor used for the battery terminals, alternator and starter tied in well with the build. The starter wire provides power to the starter and the fuse box and required no alteration. This is split to the alternator and power steering pump at the fuse box. I ended up using the power steering power to be the direct power to the Ron Francis body harness. This worked out really well and kept the wiring clean coming from the donor fuse box. The alternator needed about 12 inches spliced into it to reach the alternator.
I used the Digital Guard Dawg for my start/ignition switch. This tied in well with the harness and worked great. I even added a larger 28mm start button.
Start Circuit: Connect the start wire to a specific pin on the PCM. Fairly simple.
Ignition Circuit: The PCM relay is already wired, but there are two pins that need to be triggered for ignition and powered during run.
Fuel Pump Circuit: Use the Ron Francis, but power needs to be sent back to the fuse box to a specific splice.
DLC: Bought a generic DLC with pigtails off Amazon and then wired Power, Ground, and HSCAN+/- (Connect to two PCM wires)
Fan: PCM controlled. Only need 1 of 3 fan relays to work. Donor has it all wired, just connect to Fan relay #3 and ground.
MIL Indicator: Battery power and one pin on the PCM.
Step 4: Layout and Clean Up
I put the PCM on the passenger side up by the front of the engine and the fuse box in the corner on the passenger side close to the heater and wiper motor. I mounted the PCM on the F panel and the fuse box to the frame and top of the footbox. I used the Breeze battery tray. The combo of the PCM, Fuse Box and Breeze battery tray placed wiring in a good location for nearly everything. The wires running to the accelerator and clutch were a little long, but I just put in a loop rather than cutting out a section. Everything is wrapped in electrical tape and shrouded in loom protectors with some additional electrical tape at joints and along long runs. I bought some connectors to help with adding in stuff as needed.
Other Notable Items:
- This will require a PCM flash to get rid of PATS, Emissions etc. I found a tuner that would do this and a performance adjustment for $600. Most places wanted around $400 to do it without the performance adj., but I found a place that did mine closer to $200. James Riediger at customecm.com (
[email protected])
- No need for the emissions canister.
- Used the accelerator pedal and clutch switch from the donor
- Used rivnuts for all ground connections.
There are some more details for those interested, but I don't want this post to be too long.
If anyone is looking at doing this PM me and we can have a conversation where I can share more as needed. Eventually I will have a complete wiring diagram along with fuse and circuit layout.
Shout out to Alan_C and sparkymark for some help along the way. Thank you gentlemen.
Video (There is a light rattling I need to identify)
Thanks: 
Likes: 
Reply With Quote
Originally Posted by juddster
