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Discussion Starter · #1 ·
So I'm doing a dominator setup in my 1990 Mustang and I have been working on getting the loose wires on the main harness wired in. I wired the green wire to the tan/light green wire that goes under the hood and leads to the fuel pump relay under the drivers seat. I'm not 100% on where I want to mount the black wire, as I know it's supposed to have solid ground to both the battery and the engine. I took a look at where the negative cable on my battery led to and noticed it connected to the starter solenoid so I thought that may not be a good place to put it. If you have a good recommendation on where to connect that wire, it would be appreciated. I know the red and white wire needs to be a good 12v ignition source so I thought I could connect it to the red and light green wire that goes to the coil. The yellow wire I'd wire up to the negative on the coil. the red wire would be wired to the positive battery terminal (using a battery that has side and top post) on the battery side post along with the ecu power. The white wire won't be used because I'm using the factory coil/tfi ignition (since the factory coil is inductive instead of a capacitive discharge style system). Does all of this seem correct, all of the power sources are clean enough? No issues?

Another problem that I'm running into is, I removed the factory harness and the plug that goes onto the factory coil went with it and I sold the harness. Now I need to figure out how to wire the coil back up without the factory harness. How would I go about that? Go off the red and light green wire for power to the coil? Where would I wire the negative that connects to the coil? Does it just ground? If so, where does it ground to? Chassis? Engine?
 

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DO NOT GROUND ANYTHING TO THE STARTER SOLENOID! Only positive power at the starter solenoid.
Ground to the chassis or engine. Anywhere there is a good ground.

The EEC-IV grounds the relay to energize it and the Holley provides power so you'll need to ground the tan/light green wire at the relay and connect the red wire from the relay to Holley fuel pump wire.

If the EEC-IV main power relay is still in the car, the red wire you cut at the fuel pump relay will provide key on power for the Holley ECU.

The Holley TFI ignition harness (you did get the separate add on harness, right?) should have a white wire that connects to the negative side of the coil. Positive side gets key on power.
 

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switched sources of power are located in the fuse panel in the cockpit

use the body for grounds, use the starter relay hot post for non switched power
 

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'87 20th Anniversary Cougar7.0 427W
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I feel obligated to post a link to this thread that goes into all the details of a Holley installation in a Fox Mustang.

In addition, look for Note 2 in the above post, it's an absolutely genius way to use the OEM Ford ECU Power Relay to connect the 4 loose wires (red, red/white/black/green.)
 
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Discussion Starter · #6 ·
DO NOT GROUND ANYTHING TO THE STARTER SOLENOID! Only positive power at the starter solenoid.
Ground to the chassis or engine. Anywhere there is a good ground.

The EEC-IV grounds the relay to energize it and the Holley provides power so you'll need to ground the tan/light green wire at the relay and connect the red wire from the relay to Holley fuel pump wire.

If the EEC-IV main power relay is still in the car, the red wire you cut at the fuel pump relay will provide key on power for the Holley ECU.

The Holley TFI ignition harness (you did get the separate add on harness, right?) should have a white wire that connects to the negative side of the coil. Positive side gets key on power.
Yes, I got the separate harness.
So I won't use the yellow or white on the main harness. Ground black to battery, body, or engine.
I'm assuming my red is fine being hooked straight to the battery? Is it better to hook it to switched power?

Note: Battery has side and top posts. Positive side post powers ECU and red from the main harness is currently connected there, negative only has black from main power harness. Top posts are where everything else is connected, starter, cooling fan, ect.
 

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Discussion Starter · #7 ·
I feel obligated to post a link to this thread that goes into all the details of a Holley installation in a Fox Mustang.

In addition, look for Note 2 in the above post, it's an absolutely genius way to use the OEM Ford ECU Power Relay to connect the 4 loose wires (red, red/white/black/green.)
I have read through that thread and it is indeed genius. Unfortunately, the ENTIRE engine harness was removed.
The OEM ECU Power Relay is gone with it. Makes me wish I kept my OEM main harness.
 

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I have read through that thread and it is indeed genius. Unfortunately, the ENTIRE engine harness was removed.
The OEM ECU Power Relay is gone with it. Makes me wish I kept my OEM main harness.
I am not sure how good an idea it is as I'm currently trying to figure out how to remove the OEM harness trough the firewall. Seems that relay or something is stuck and I can't get it out. How did you do it? Also, what he did requires keeping the majority of the OEM harness (salt n pepper and O2 harnesses can be removed). But then how does one fit the new holley harness through the firewall?

I'm stumped and frustrated at this point. I probably should eat something and think about it some more :D

I definitely can't reach up there to grab that relay, yet that part of the cable won't move, like it's attached to something that I can't reach. D'oh.
 

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Discussion Starter · #9 ·
I am not sure how good an idea it is as I'm currently trying to figure out how to remove the OEM harness trough the firewall. Seems that relay or something is stuck and I can't get it out. How did you do it? Also, what he did requires keeping the majority of the OEM harness (salt n pepper and O2 harnesses can be removed). But then how does one fit the new holley harness through the firewall?

I'm stumped and frustrated at this point. I probably should eat something and think about it some more :D

I definitely can't reach up there to grab that relay, yet that part of the cable won't move, like it's attached to something that I can't reach. D'oh.
Getting the main harness out sucked, I managed to get the relay out first. Getting the 60 pin connector out was the hard part because it's quite large and the wires make a sharp turn. I think there is a little clip thing that holds the relay in place. I was in and out of the passengers side of the car trying to persuade the harness to come out. I had the glove box removed, I don't remember if that helped or not though.

Once I got the OEM harness out, feeding the Holley harness from the engine bay into the car was easy. The plugs are WAY smaller than the factory 60 pin connector. You can easily run the main harness and the power harness through with no problems.
 

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Yes, I got the separate harness.
So I won't use the yellow or white on the main harness. Ground black to battery, body, or engine.
I'm assuming my red is fine being hooked straight to the battery? Is it better to hook it to switched power?

Note: Battery has side and top posts. Positive side post powers ECU and red from the main harness is currently connected there, negative only has black from main power harness. Top posts are where everything else is connected, starter, cooling fan, ect.
Red to battery. Red/white wire is for switched power.
 

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I am not sure how good an idea it is as I'm currently trying to figure out how to remove the OEM harness trough the firewall. Seems that relay or something is stuck and I can't get it out. How did you do it? Also, what he did requires keeping the majority of the OEM harness (salt n pepper and O2 harnesses can be removed). But then how does one fit the new holley harness through the firewall?

I'm stumped and frustrated at this point. I probably should eat something and think about it some more /forums/images/smilies/biggrinnew.gif

I definitely can't reach up there to grab that relay, yet that part of the cable won't move, like it's attached to something that I can't reach. D'oh.
Getting the main harness out sucked, I managed to get the relay out first. Getting the 60 pin connector out was the hard part because it's quite large and the wires make a sharp turn. I think there is a little clip thing that holds the relay in place. I was in and out of the passengers side of the car trying to persuade the harness to come out. I had the glove box removed, I don't remember if that helped or not though.

Once I got the OEM harness out, feeding the Holley harness from the engine bay into the car was easy. The plugs are WAY smaller than the factory 60 pin connector. You can easily run the main harness and the power harness through with no problems.
There's a ton of harnesses and connectors in my passenger kick panel. In addition, part of the massive harness splits off after going through the firewall and goes into a channel running down the passenger side. I assume there's no connectors on this so the premium sound gets direct power.

Edit: in addition, turns out the fuel pump relay in on the passenger side rear quarter.

This special edition 20th anniversary cougar has every option Ford ever made, so I also have 2 additional connectors on the main harness, seems like for dealing with the full electronic digital dash. Looks like I'll be manually going through the main wire by wire, thus I'll have a sub harness in addition to the Holley harness when I'm done. Fortunately I have a full wiring book for this model car, good thing I checked because there's no possible way to pull my harness through without unwrapping it completely and cutting wires.
 

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Discussion Starter · #12 ·
Red to battery. Red/white wire is for switched power.
Since I have no main, o2, or engine harness, is it best to just make a new circuit for red/white in the fuse block?

Since I also no longer have the coil plug and need to get a new coil plug and get it wired up, would you also suggest making a new circuit just for the coil?
 

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Discussion Starter · #13 ·
There's a ton of harnesses and connectors in my passenger kick panel. In addition, part of the massive harness splits off after going through the firewall and goes into a channel running down the passenger side. I assume there's no connectors on this so the premium sound gets direct power.

Edit: in addition, turns out the fuel pump relay in on the passenger side rear quarter.

This special edition 20th anniversary cougar has every option Ford ever made, so I also have 2 additional connectors on the main harness, seems like for dealing with the full electronic digital dash. Looks like I'll be manually going through the main wire by wire, thus I'll have a sub harness in addition to the Holley harness when I'm done. Fortunately I have a full wiring book for this model car, good thing I checked because there's no possible way to pull my harness through without unwrapping it completely and cutting wires.
There doesn't happen to be any other weird plugs that need to be unplugged?
I wish you only the best of luck getting it out.

I couldn't help but to notice you're running a 428 Windsor in your Coug,
How do you like it?
 

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There doesn't happen to be any other weird plugs that need to be unplugged?
I wish you only the best of luck getting it out.

I couldn't help but to notice you're running a 428 Windsor in your Coug,
How do you like it?
I love the new engine. I got the Holley to ensure I can get the most out of it and help protect it using knock control.

Now, back to this wiring. Ugh, the picture shows two harnesses going through the firewall, but it's actually combined into one round harness to fit through the single hole in the firewall grommet. Hoping I can separate them somehow. Also hoping I can figure out how to access the screw that holds the EEC power relay shown in figure to left below.

 

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Turns out the Figure in the above post was incorrect and the split cable included the EEC wires and wires from the EEC to the EEC power relay (out->in), other power relay wires and fuel pump relay wires. I'm extremely pleased now as this is a simple exercise to wire things up now - I'll probably just run a new power wire for the fuel pump (yellow in pic) and same for always hot needed for Holley (red on HP). I can route these through the separate Holley power cable that connects directly to lugs on the side post part of my dual-post battery (tie them into a single or two ring-lugs.)

Anyway, I did have to lower the glove box (didn't need to remove it completely) to get to the EEC Power Relay. This was fun as a 1st project of the day as it was difficult to get my fat hand into the spot and a wrench. Turns out I had to use one of those tiny box wrenches that had a 9/32" on one end. I turned it like 35 1/4 turns until that stupid green fine threaded bolt came off. I was pleased that I had to put two band-aids on my left wrist as the lip of the dash edge slowly rubbed off my skin until it was oozing blood. :pain: Good thing I don't have a therapist, I might be put into the funny farm :lol:



I'm going to guess that most people wouldn't be extremely pleased looking at this mess, but I was ecstatic. There's so much add-on junk that I get to remove now - the list is long:

1. Add on loose wiring for Mass Air conversion.
2. Wires tapping into EEC for DataQ data acquisition
3. Wires feeding through for 2-step and shift light (I may keep these from my ignition box if it saves me I-O's on the HP)
4. EGR wiring tapped into for use as boost gauge (damnit, that's what those wires marked "1" "2" and "3" go to that I cut :( )
5. USB and switch cable for TwEECer.
6. Wires also tapped into for data acquisition through LM-1 wideband

I think that's all :lol:

 

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Discussion Starter · #16 ·
Whoa, it's been a while since I've heard anyone mention using a DataQ!
I have one of those for logging with a Moates Quarterhorse but never ended up needing it.
Did you end up getting your harness removed?

I have made exactly zero progress. Long work days do well to curtail my ambitions.
Hopefully tomorrow will bring at least a little progress.
 

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Whoa, it's been a while since I've heard anyone mention using a DataQ!
I have one of those for logging with a Moates Quarterhorse but never ended up needing it.
Did you end up getting your harness removed?

I have made exactly zero progress. Long work days do well to curtail my ambitions.
Hopefully tomorrow will bring at least a little progress.
I got the harness removed, labeled the connectors and individual wires so I can rewire efficiently as I can. I know these connectors don't align with a Mustang, though perhaps something I'm doing will help. I rerouted oil pressure gauge through the C317 connector so both ECT and oil pressure now jump from drivers side fender apron (through C312) directly to engine. The C315 takes -coil feed in for tach - so only one terminal needed on that connector. C294 has switched power (Red/Lt Grn) for +coil and Holley Red/White which I'll run through the Holley power cable sheathing.

 

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Discussion Starter · #19 ·
I got the harness removed, labeled the connectors and individual wires so I can rewire efficiently as I can. I know these connectors don't align with a Mustang, though perhaps something I'm doing will help. I rerouted oil pressure gauge through the C317 connector so both ECT and oil pressure now jump from drivers side fender apron (through C312) directly to engine. The C315 takes -coil feed in for tach - so only one terminal needed on that connector. C294 has switched power (Red/Lt Grn) for +coil and Holley Red/White which I'll run through the Holley power cable sheathing.

I only got the ground done on mine today. I didn't have time to do much so I wired the black wire to the chassis ground that is attached to the drivers side head. I know there is a red/light green wire that is supposed to go to the coil and tfi module (on the OEM main harness), that wire traces back to a fuseable link and then back to the ignition system. I can't seem to find where it goes back to. I can only think of four plugs it could go back to (unless I'm missing something). Two plugs that are near the ECU on the inside of the car, and two plugs that are on the drivers side. I looked closely at the wires that go to the two plugs under the hood and didn't see red/light green. I looked at the ones inside the car and there appears to be a pink and light green, but no red and light green. I may explore the possibility of making two new circuits in the fuse block.

I guess I'll see.

How are you wiring your coil up?
Is my assumption that you lose your coil plug when you remove the main harness correct?

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
If you look at the TFI connector on this diagram you can see the red/light green wire coming off.

If you look at the attached picture you can see the the ignition switch, link, and red/light green that goes to the coil and TFI.
Now where on earth does the red/light green go back to so I can connect my coil?
Maybe the dark blue wire after the link?

It's hard to tell where the harnesses plug into each other and where one one harness ends and another begins.
 

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I only got the ground done on mine today. I didn't have time to do much so I wired the black wire to the chassis ground that is attached to the drivers side head. I know there is a red/light green wire that is supposed to go to the coil and tfi module (on the OEM main harness), that wire traces back to a fuseable link and then back to the ignition system. I can't seem to find where it goes back to. I can only think of four plugs it could go back to (unless I'm missing something). Two plugs that are near the ECU on the inside of the car, and two plugs that are on the drivers side. I looked closely at the wires that go to the two plugs under the hood and didn't see red/light green. I looked at the ones inside the car and there appears to be a pink and light green, but no red and light green. I may explore the possibility of making two new circuits in the fuse block.

I guess I'll see.

How are you wiring your coil up?
Is my assumption that you lose your coil plug when you remove the main harness correct?

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
If you look at the TFI connector on this diagram you can see the red/light green wire coming off.

If you look at the attached picture you can see the the ignition switch, link, and red/light green that goes to the coil and TFI.
Now where on earth does the red/light green go back to so I can connect my coil?
Maybe the dark blue wire after the link?

It's hard to tell where the harnesses plug into each other and where one one harness ends and another begins.
OK, phew, I think I figured it out or you. The wire in the Brown 8-pin #31 connector (between shock tower and firewall, drivers side) is red/green versus red/light green, but this diagram below shows that the switched run/start circuit comes into the engine bay as red/green. I'm assuming after the fusible link (N) it perhaps became red/light green? Anyway, I'm a poor reader apparently and I now see how you don't have access to the original harness (you stupidly sold it :lol: ) so you can't verify this. One good thing is the diagram for '91 - '93 EEC pinout on veryusefulinfo does show red/grn as going from ignition switch to EEC Power Relay, which we know also connects to TFI and coil positive. Note that tan/yellow in the 2nd image below connects from TFI to negative coil - it's what triggers your spark pulses, very important. It can also connect to your tach through the brown #31 connector, as you can see in the 1st image. I think this should just about square you away now...



 

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