( copy and pasted from some ford forum)
Much of this electrical info came from Darrell Jermain off the Carb'd Mustang Mailing List. (Thanks for the info Darrell!! - Fletch)
Your car is divided into two harnesses; the EEC harness and the main or "chassis" harness. The EEC harness contains all of the computer related sensors, actuators, and such. It also contains some of the wiring for the air bag system. The chassis harness contains everything else; headlights, fuel pump wiring, instrument cluster, etc., etc. In order for the EEC to receive power from the battery, control fuel pump, and the airbag to work properly, the two harnesses must mesh together at some point. There are 4 of these points:
--Two connectors near the computer (passenger-side kick panel). One is green, one is gray. Both are 8-pin connectors I believe. One is rectangular and the other is round.
--Two connectors near the driver's side hood hinge and right above the master cylinder. One is gray, one is black. They are both round, 8-pin connectors. One of the connectors does not utilize all 8 pins.
The first thing to do is the part that's the most fun! LOL Disconnect the battery (of course!). Remove the computer and the EEC Power relay that sits directly above the computer. On the 60-pin connector that plugs into the computer, remove the black plastic "cap" which holds the wire bundle at a 90 degree angle to the connector. Unplug the two 8-pin connectors mentioned above, unscrew the bare wire ground and you should be able to pull the harness up into the engine compartment. The oval-shaped grommet will come with the harness, so use a screwdriver to pop it out of the hole.
Once you've got that done, everything you need to remove is under the hood. Just start at one end of the harness and work your way around and disconnect everything you come to that attaches to the EEC harness. As a minimum, you're going to have to remove the upper intake to get to all this. This should include the following items:
--TAB/TAD solenoids
--EVR solenoid
--MAF meter
--Air Bag connector below MAF
--Round 8-pin connector below MAF
--EVP solenoid
--TPS
--IAC
--All 8 injectors
--Water temp sender
--Oil pressure sender
--TFI module
--ACT
--ECT
--Carbon canister solenoid
--ground at starter solenoid (single pin connector)
--Two connectors located near brake booster
I'm sure I'm forgetting something, but just disconnect everything you come to and the entire EEC harness will pull out. You will be shocked at how much all that copper weighs..LOL
Once you've got everything out, it's time to start re-wiring. All the re-wiring will take place at the two connectors by the brake booster that you unhooked earlier. This is how you will tap into the chassis harness and get things like the fuel pump working again. Best way to accomplish this is to tap into the wires just below the connectors. I use those little plastic splice connectors...works great. Be sure to tape up the open ends of the connectors to prevent water from getting in there.
If you've got a Chiltons with the wiring diagrams in it, I will include the reference numbers for each wire if you'd like to look them up.
On the Gray Harness:
---Wire #16 (red/light green - 16 Ga) to the ignition trigger/turn-on lead. On my MSD it's the thinner red wire.
---Wire #11 (Dark Green/Yellow - 20 Ga) to the negative side of coil or the "tach out" port on an MSD. This is the line to your stock tach.
On the Black Harness:
----GROUND #97 (tan/light green - 18ga) to a suitable chassis ground. This creates the ground for the primary side of the fuel pump relay.
---Wire #39 (red/white 20ga) to the temp sender.
---Wire #31 (white/red 20ga) to the oil pressure sender.
---Wire #361 (red 16ga) to #16 (the wire you ran to the ignition turn-on above). This creates the positive voltage supply for the primary side of the fuel pump relay.
My car already had A/C delete, so I didn't mess with the WOT cut-off. Only other thing that you need to do is when wiring in the fuel pump itself. Just get the polarity right on the two wires that are coming off the stock EFI pump. I cut them and extended them out to where my Holley Blue is.
On the underside of the car, you can disconnect the O2 sensors and oil level sensor (side of oil pan) and pull that harness out too. I didn't mess with it, but you could rewire the oil level sensor to still be operational if you wanted.
After that, you should be good to go! As far as wiring the ignition, you'll have to run wires to the positive side of the battery and chassis ground as well as wire the pickup to the distributor. If you've got an MSD, the diagram can be found at:
http://www.msdignition.com
Just in case you didn't know, the smaller the gauge (Ga) of a wire, the bigger around it is. That should help you to distinguish between the right wires. Your fuel level gauge will still work properly (providing you didn't put an old carb tank in the car) and your ammeter should work fine as well.
