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A few wiring harness questions

Got an 87' GT I just stuck a 2002 4.6 2V into...
On the starter harness, what does the single connector by the starter connectors, connect to? Also, if I'm not using an engine fuse box, what do I do with the wire that bolts to the stud of the fuse box since its hot? Cut it off?
I left the foxbody body harness in place. Is there an easy way to apply power to the original body harness for the windows and lights to still work? I'm using an Autometer gauge cluster, so my gauges will work as long as my body harness is powered.


Active Member
If you could take a pic of the starter connection, that would help a lot. Or what color the wire is.,
Is this on the fox harness, or the 2v harness? If it’s the fox harness and fox starter solenoid, the single wire should attach to the small terminal on the solenoid. Usually red/light blue wire. This is the trigger wire that engages the solenoid and sends power to the starter.
Comes from the ignition switch, then through clutch switch (Manual) or neutral safety switch (auto) and on to the starter.

Wire to stud on fuse box should come from alternator. If you are not using the fuse box, you can remove the wire and attach the fox alternator wire to the alternator (black and orange)
Fox body harness should have a yellow wire with ring terminal that bolts to the always hot side of the starter solenoid. This should give you headlights, brake lights, hazards, dome light with key off, and should power all the other stuff with the key on.

Sounds like a cool build, do have a build thread?
For the starter harness I'm using the 2v harness. By the battery terminals, there's a few grounds, and a few connectors that come off the hot side. I'm guessing a few of these would normally goto the fuse box? Also on this same harness, about half way through it, where it goes under the engine is what appears to be a ring terminal ground, and a single connector, but there are no sensors or anything in that area. I'm thinking maybe charcoal canister? And then at the end of the harness are the 2 starter connections.

So you're saying I can connect the orange/black fox alternator wires to the 2v alternator? To the ring terminal? Are these the same wires that run to the amp light in the cluster to excite the circuit, or is that even necessary? Does the 2v harness excite that circuit?
And then run the yellow wire ring terminal from the fox harness to an always hot source?
Also, another question, on which harness is the speed sensor(99+ T45)? It doesn't seem to be on the engine harness.

I haven't started a build thread yet. I was waiting til it's either done or very close. I've got the everything done except the wring. The 2v harnesses are ran, just need to mate it with the fox, body harness. It's got a 2002 explorer aluminum block 4.6 that I found for cheap, and it had just been rebuilt. Converting the explorer block to work required some extra steps, but nothing major. I can definitely tell the weight difference. My front end now sits about 2-3" higher than it did before I yanked the 5.0 out.
Something else I thought of... should I just put a fox starter relay back in place, and run that hot terminal from the starter harness to it, along with the fox harness wires that need a hot connection?


Active Member
Well, again, a pic of that single connector will go a long way towards identification.

If you use the fox starter solenoid, it could be used as a distribution block, like it was in stock configuration. Run + battery cable to the top post, also attach yellow wire with ring terminal to top post, like it was from factory. This should power up your “always hot” circuits.
“key hot” circuits should also work, but obviously goes through the ignition switch.
2v starter should have its own solenoid, so you would be using the fox solenoid only as a common mounting point for constant 12v power.

I would assume the vss would be on the transmission harness, not 100% sure tho.

When it comes to wiring especially, posting up pics becomes really important because otherwise we are just guessing.
Do you have wiring diagrams for both vehicles? If not, I highly recommend that you either purchase or download them.
Also, a test light and voltmeter are necessary pieces of equipment to have in this situation.
This will allow you to test for power, ground, and continuity of all circuits.

My car is a 79 and yours is an 87, so I can give you the info that I know is correct for my car. Yours is probably similar but might not be exact.
On my car, the black/orange from the alternator goes through a fusible link, then splits and goes to the fuse box, as well as the headlight switch.
Looks like the later years may have that circuit going through a fusible link, then fuse box, then light switch, no split.

Using a voltmeter set to continuity, you would be able to identify the “other end” of any wire, as well as any other wires connected to that circuit.
Good luck!
Looking at transmission harnesses on eBay, I'm not really sure why I would need one. My engine harness has all the O2 sensor connections and the reverse lights connector. Maybe I need to go back and double check that it didn't get cut off or something.
Here's a few connections I have questions about...
On the starter harness, this red/white wire. What does it connect to?

Coming off the 2v engine harness, this orange/black and green wire with a ring terminal. Do I connect that in with the hot side of of my starter solenoid? Also the fox red/blue ignition wire, is that necessary?

Also on the starter harness negative side is this connector. Cant find anything it might connect to? Is it an ECU ground like fox bodies used?

Part of the fox harness, these three wires I believe used to be on the hot side of the starter solenoid. Are they still used for anything?
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Another issue I can't figure out is the OBD2 situation. I have a dash harness which has the OBD2 port. It connects to 2 of the connectors by the ECU. I tested continuity of the wires going into the OBD port to where they connect by the ECU. Some of the wires don't run through that connector. The black/yellow signal return wire runs to another connector up by the fuse box. What exactly does that signal return wire goto? Is it not necessary?
Also is the body harness necessary? It's a giant rats nest of wires I don't really have the room to accommodate. The dash harness alone will be hard enough to properly conceal.
With the speed sensor, I can't find the connector anywhere. Any issues with just buying a pigtail, and then running the wire to the ECU?


Active Member
One thing that is messing me up, is your late fox has all the electrical stuff on the pass side, my early fox has everything on the drivers side lol.
To use a modern alternator with fox gauges, I think the external voltage regulator should be changed, to something like this

I’ll do a little searching on your harness to try and answer some of your questions.
I am OBD-I so can’t help much there, but pretty sure there is a fuse that affects the OBD-II port. I think that should be on the body harness? A wiring diagram will answer all of your questions.


Active Member
3 wires accounted for lol

on the black wires-
if those wires have continuity with negative battery terminal, then they should be grounds

Notice that there are 2 fuses the charging circuit goes through, a 20a and a 40a both found in underhood fuse box.
Running without these fuses may end up burning up wires, maybe not. Not sure why you would not want to use that fuse box since it contains circuit protection for many circuits.
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I'm actually using an Autometer gauge cluster I built, so the gauges all have their own signal wires going out to a sender. The alternator wire that ran to the "amp" light in the cluster had to be spliced and soldered with that resistor that was in the amp light. I'll have to look through the fox instrument diagrams to see if that's still necessary.
2 of those 3 wires are unused alternator wires. The other one seems to be a "sense and switch" wire, guessing that'll be unused as well.
I was looking at the PCM pinout thread, and one of them pretty much explains what I need to do as far as the OBD2 port and fuel pump. I just still don't understand the sig-return wire. The other thread says to ground it with the ground wire. Seems odd.
The battery/starter harness has the red wire that runs down to the starter. Along with it is a smaller red/white wire. That appears to connect to what would have been the fuse box? Where should I run that wire to?(none of my harnesses came with an underwood fuse box)
How did you run your ignition?
I've got most of the wiring figured out. On the fuel pump, I'm looking at the 4.6 harness mod where it talks about what pins to use to ground the fox fuel pump relay and tap for power. Just to be clear, splicing into the pink/black wire would be the ground right? And it also says to tap into the dark green/yellow wire at the inertia switch for fuel pump power. Would that be the same as tapping the red/black wire at the relay?


Active Member
Since I am using a stripped-down 4.6 body harness on a much earlier fox, I can see that our builds are quite a different from each other.
My engine, transmission, ECM, and chassis wiring are all from the same donor car.
I did this to eliminate all the issues that you are currently having.
My plan is to use the stock fox wiring for the chassis: lights, dash, wipers, etc. and then just add all of the engine/trans/fuel pump ECM and wiring as a separate standalone system.
All I have for 4.6 wiring going to the rear of the car is the fuel pump and inertia switch wiring. I will be using the 4.6 underhood fuse box since it already contains all the fuses and relays necessary to run the 4.6.

It looks like your ECM, engine, and engine harness are all from different model years so that may add to the complexity of the build when trying to figure out the different circuits.

IMHO you have made your build harder than it needs to be by not using matching model year harnesses. It’s totally possible and you are doing a great job with it BTW. I just wish I had more answers for you lol
Yeah I think every single harness I have is from a different year, and even model. I know the dash harness was from a v6, but I only ended up using the datalink connector from that anyways. Luckily everything else at least has matching connectors and wire colors. I think I have finally finished up all the wiring.
If any of this sounds incorrect or way off, please correct me lol
For the datalink connector, 3 wires stay untouched and run back to the ECU through the one connector of the dash harness that I kept. 2 wires got grounded, and another taps into a fused constant power source. One of the wires is unused apparently.
For the ignition, I basically set it up the exact same way it was on the fox... all the power wires/big starter wire goto one post of the starter solenoid, then the small starter solenoid wire to the other post, and the small ignition wire to the top. Still need to test it. It wasn't working earlier, but I think my clutch safety switch might have something to do with it. From the old fox wiring, I have the yellow wire which powers all the interior stuff, the black/white wire which is the power window fuse apparently, and the dark blue wire which I'm not 100% sure what it does, all going to the power side of that solenoid post.
For the charging system, I traced out the lt green/red wire from the alternator connector, and spliced it into the old fox harness wire that goes to the amp light.
For the fuel pump, on the relay under the seat, I cut the tan/lt green wire and ran it from the relay to the wire from the ECU that supposedly sends the ground signal. I also spliced into the red/black power wire and ran that to the wire from the ECU that supposedly provides power to the pump. I say supposedly b/c when I turn the key to on, the pump doesn't prime. Guess I need to do some testing with the dvom to see if any of those things are actually happening.
I also had to buy O2 sensor extensions. The passenger side front was nowhere close to being within reach. The rears have MIL eliminators on them and I plugged the holes on the X-pipe.
I left my electric fan wiring the same way it was wired up with the foxbody stuff. I have the SVE fan kit from LMR.


Active Member
Again, it’s hard for me to say exactly since your wiring will be a lot different than mine.
The data link I am just keeping mine intact. for the ignition, you are using the fox solenoid, but I think the 2v starter will also have its own solenoid. You might be able to splice the ignition wire and send power from the ignition switch, to both solenoids. Or you could run a cable from + battery terminal to the solenoid on the 2v starter and run the trigger wire to the 2v starter instead of using the fox solenoid. My underhood fuse box has starter relay and fuel pump relay already there so I will be using that for simplicity. I know what my wire colors are, but not sure what yours are so hard for me to say with confidence. Don’t want to give out any bad advice