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stand alone harness


Active Member
Can someone break down how to convert my stock 4.6 wiring harness to a stand alone? Is it fairly simple to do because I really dont feel like spending $1k on the ron francis wiring harness. I have the complete engine harness and pcm from the 97 mark motor and it is going in a 89 lx.
Thanks for the help,


Well-Known Member
Staff member
Trimming down a Modular harness to a stand-alone isn't difficult, just tedious. First you need to get the Electrical/Vacuum Troubleshooting Manuals (EVTM) for both your Mark 8 engine and for the Mustang. You also need a good ohmmeter.

Once you've got the EVTM for the Mark 8, on paper trace each wire that goes to the Powertrain Control Module (PCM, often called the computer) AND the other end of each wire to determine where it goes. If there's a Constant Control Relay Module (CCRM), trace that too. You have to keep everything that connects to the engine (and transmission, especially if it's an automatic tranny) and also the power source(s) and grounds for the PCM. Some of the other things controlled by the PCM, such as cruise control and air bags, you can either keep or delete depending on your needs and wants.

Once you've determined what to keep, you can start removing all the extraneous wiring for lights, horns, windshield washer, etc., since the car is already wired for them. Before you cut a wire, find both ends of it and check for continuity (zero 0hms) to make sure you've got the right wire.

After you've trimmed the Modular harnesses down to stand-alones, go to the EVTM for your Mustang and determine where to connect the stand-alone harnesses to the existing wiring. See the thread titled "Mod Motor Wiring in General" under the Electrical Wiring section. The diagram there will give you an idea of the wiring harnesses under the hood and how they connect to each other. There may be some differences with the Mark 8, but the general concept is the same.