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Discussion Starter · #1 ·
is it possible to use the just the computer harness(FMS-M12071--C302) from the doner/summit racing and the painless wiring kit for the dash, lights, etc. my feeling is i can but wanted to check with those in the know and have done this. one of these days maybe i'll answer a ? instead of asking.
 

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I have the exact same question. My donor is an 85 GT that was carburated and is now fuel injected with a 91 computer, intake and all sensors. I had to splice all the wires for power and the fuel pump, which wasn't that hard with a wiring diagram for my car and the 91 computer. Hopefully someone knows. Nick
 

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Suggest you stay with all donor harnesses, pay the $400 for getting the diet wire stripping/testing andlabeling done. The Ford wiring harness is good quality and Roger Stine or one of the others will give you very good value. The dash is not that difficult to wire with the stripped donor harnesses.
 

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Here is my experience, for better or worse, you decide: I did my own harness diet. My intent was to only have the EFI harness and to do my own lighting and dash harness. I bought the Helm manual for my year donor. I did not touch the on-engine harness (I needed all that stuff anyway) The off-engine computer harness I completely unwrapped, tossed all the split-loom (I hate that stuff) and unzipped the plastic tape.
Spent the next 2 nights traceing wires from the computer connector out, with a pair of cutters and masking tape. Labled everything first. Then... Cut out the A/C related stuff. Low oil and clutch safety? Out the window. All the main wiring harness connectors? Right in the trash. Giant cutter sliced the main harness in half so I could get the grommet for the firewall. (yep, I sweated a bit on that one)Stripped the fuel system portion out of the rear harness and tossed the rest of that one too. Did *NOT* touch the portion of the harness to that went to the ECC power relay. Replaced my solenoid with an aftermarket one with an ingnition post. Hooked up TFI 'start' power to the ignition post. ECC power Relay and TFI Power to a Run/Stop switch. ECC and Coil power, Fuel Pump Relay +, Fuel Pump +, and HEGO + to power source. Keepalive to battery. ECC Grounds as needed. Oil pressure sender to gauge, Water temp sender to gauge, coil return to tach. Sat back, crossed fingers, and hit starter button. Engine fired on the first try. Wrapped everything in friction tape (it's now waterproof) It's not rocket science. Fun? no. Time consuming? yes. Scary? A little. And yes, I was goaded into it by a buddy of mine here at work that did a conversion of a bronco from carb to FI years ago, basically doing the same thing. I've still got the lighting to do, as well as the remainder of the dash harness, but the engine purrs just fine.

[and for those that are wondering, yes I used appropriate fuse links and/or Circuit breakers as needed ]

Mike
I'll need 2 more wires off the harness before I'm done (VSS +/- for my speedo, Autometer electronic)
 

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Ed, I did the exact thing you're asking about. If you are an electrical idiot, which I are, this is a hard job. If you understand electricity and have electric experience, I think it's a piece of cake.

The thing you most need is the $5 Ford Racing book: "Multiport EFI Engine Management Harness-Wiring Harness Installation Manual" part # ISM-12071-C302. I think you can get it from Mike Forte or another FRPP dealer, or through the Tech Hotline # they give in the book: 810-468-1356. This book tells where to hook up every wire in the factory harness. The book is designed for guys using Ford EFI in hotrods, etc. You can use it to splice into the appropriate Painless Harness wires you get from FFR.

BTW, you'll need more than just the main harness M-12071-C302. Probably figure on the Sensor-relay package (D302), Engine harness and controls (E302) and Speed Sensor connector (J302). Mike Forte talked me through this whole thing, it's not as confusing as it sounds at first!

An alternative is to buy the Painless Ford EFI harness, that's designed (I believe) to mate with the Painless frame harness you get from FFR. I have NO experience with this, but have heard Mike Mack uses it on his Tristate Motorsports builds, so that's one guy you could check with for more info...I bet he sells em too if you decide to go that route.

Personally, I LOVED my first FFR build, where I used the entire Mustang wiring harness, plugged everything in and it worked perfectly from Day One. I cursed myself for going the Painless route on this new car because I was lost a few times...being an electrical dimwit. BUT, I got some help at critical points from Doug Huey, who is a master, and am very happy with the final result. I figure my inadequacies with the Painless harness slowed down my build by 2 weeks or so. Next time for me: Donor harness stripped down by one of the wizards, so it's plug and play when I install it.

Sorry this giot long, hope I helped.
 
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