Holley Harness (or similar) for G-body anyone?

RED LS1

SENIOR MEMBER
Here's where i'm at with my swap right now.

It's an '87 GN. I removed the Passenger side inner fender and factory LC2 Wire harness. I am going to be running a Holley Dominator EFI and I am going to buy the LS Harness for it shortly. If any of you guys are running this setup or can comment on a different harness please respond.

What I want to know is how you ran it through the firewall? Can I retain the factory grommit and bracket and run the Holley harness through that ? How much of it goes through and into the EFI box? How far into the cabin does the LS HArness go? Can I mount the new ECM in the old G-body ECM cover?

Thanks for any insight. I'd like to get the harness through and get the inner fender back in to move on to the next thing.
 

Chuck Leeper

Toxic old bastard
Staff member
Dominator box is too big to fit the orig box.
I ran mine under the console w/ the box under the pass seat. The harness goes thru a hole at the top of the trans tunnel.
I had to shorten several sensor wires, in order to get it to look good.
I have a 4L80E. I used the Holley harness and ran it thru the base of the tunnel, at the rear of the seat mount.
The main power wires HAVE to go directly to the batt. Mine is in the trnk, so I ran them along the door sill and over the wheel well.
If I was to do another, I'd buy the unterminated harness, and then cut to length. MUCH easier. I was lucky, I work at a wiring shop, so I had all the pins to do the connector mods.

I can send you some pics, if you want. Send me your email addy.
 

RED LS1

SENIOR MEMBER
Dominator box is too big to fit the orig box.
I ran mine under the console w/ the box under the pass seat. The harness goes thru a hole at the top of the trans tunnel.
I had to shorten several sensor wires, in order to get it to look good.
I have a 4L80E. I used the Holley harness and ran it thru the base of the tunnel, at the rear of the seat mount.
The main power wires HAVE to go directly to the batt. Mine is in the trnk, so I ran them along the door sill and over the wheel well.
If I was to do another, I'd buy the unterminated harness, and then cut to length. MUCH easier. I was lucky, I work at a wiring shop, so I had all the pins to do the connector mods.

I can send you some pics, if you want. Send me your email addy.


Thank you. So than you don't have any of your harness ran through the factory firewall hole? You ran it under the car through the trans tunnel? It's just hard to think this out without the harness in my possession.

What did you do for the few factory wires from the OG lc2 harness that needed to remain? Caspers told me he could make a new set that has just the necessary wires to get the cluster and body harness working for $45.
 

Chuck Leeper

Toxic old bastard
Staff member
Thank you. So than you don't have any of your harness ran through the factory firewall hole? You ran it under the car through the trans tunnel? It's just hard to think this out without the harness in my possession.

What did you do for the few factory wires from the OG lc2 harness that needed to remain? Caspers told me he could make a new set that has just the necessary wires to get the cluster and body harness working for $45.

The harness does not run under the tunnel. It lays along the console on the interior floor.
No, I did not use the oem hole.
I have a custom dash, so I had no need for the oem harness.
 

RED LS1

SENIOR MEMBER
If you have some pics I'd like to check them out. This was helpful. It sounds like you set the harness up and routed it through the places in the trans tunnel that worked out best.


Thanks
 

Chuck Leeper

Toxic old bastard
Staff member
If you have some pics I'd like to check them out. This was helpful. It sounds like you set the harness up and routed it through the places in the trans tunnel that worked out best.


Thanks
Just sent you some pics..NO! The harness does not go thru holes in the tunnel. It goes thru the hole I made in the firewall right at the end of the trans tunnel. The only hole I made in the tunnel is for the trans harness.
[You have to buy the trans harness separate. It does not come w/ the main harness.
 

RED LS1

SENIOR MEMBER
Ok, I understand. Yeah, i'm aware of the harness being separate for the trans. I work for a large transmission shop so I'm going to pull a fresh 4L80 to throw in. What engine mounts and trans X-member did you use? I'm looking at the BRP hotrods (i think) that's like $450. It's a lot of money but I just want a bolt in part with no fab needed. That's worth a little more to me.
 

RED LS1

SENIOR MEMBER
Was that harness that long when you got it? I'm referring to the length that is running from the box to the firewall. That's a pretty good length. What's all the stuff under the console? Is that required for the Dominator box or is that a central location you chose to tie ALL of your upgraded electronics together?
 

Chuck Leeper

Toxic old bastard
Staff member
That is the length of the harness when I got it.
The other "stuff" is the controller for the trans indicator on the dash.
Dominator power supply relay, etc.

What engine are you going to use? I have a harness that I didn't use. I can post the pt # if you want to cross reference it on the Holley site.
 

RED LS1

SENIOR MEMBER
It's a 4.8 Gen 4 LS. If the harness is a new Dominator LS harness it should work? I don't think there's multiple ones accept for the reluctor maybe. I think mine is 26X or something i'd have to double check.
 

Chuck Leeper

Toxic old bastard
Staff member
It's a 4.8 Gen 4 LS. If the harness is a new Dominator LS harness it should work? I don't think there's multiple ones accept for the reluctor maybe. I think mine is 26X or something i'd have to double check.
I it's a gen4 engine, it should have the 4x cam sensor located at the ft of the timing cover. The knok sensors will be on the side of the block, and the crank sensor should be 58x.
 

RED LS1

SENIOR MEMBER
I just looked at the PM from the guy I bought it from. He said it had 24x cam and crank sensors. I'm pretty sure the knock sensors are in the intake valley pan as I have the intake off now and it has the 2 sensors with the harness out the back. The front cover does have a place for a sensor. It is suppose to be an '07 4.8 with LS9 Cam. It has 799 heads and LS1 Intake manifold.

 

RED LS1

SENIOR MEMBER
Chuck,

Here's a picture of my firewall how it sits. Can you give me an idea where your harness came through? Also, I may have already asked this but now that I pulled the og harness out I have the question again. Do you have anything coming from the fuse box bulkhead where the original engine harness came out? Or did you just unplug the factory engine harness and that's the end of it? I've been told there's a few wires from that harness that need to remain for the car to run. Like starter wires maybe?


 

Chuck Leeper

Toxic old bastard
Staff member
Didn't I send you some p
Chuck,

Here's a picture of my firewall how it sits. Can you give me an idea where your harness came through? Also, I may have already asked this but now that I pulled the og harness out I have the question again. Do you have anything coming from the fuse box bulkhead where the original engine harness came out? Or did you just unplug the factory engine harness and that's the end of it? I've been told there's a few wires from that harness that need to remain for the car to run. Like starter wires maybe?


Didn't I send you pics of the layout, and where the harness comes thru??? Isn't your email addy justinpa81@gmail.com??
If you want the headlites, etc to work you can't just unplug the firewall plug. It's in 2 pcs.
1 side is the old engine side, and the other is the ft lites, etc.
You can open it up and remove the old wires to the engine harness, except for the main pwr wires that go to the starter. They are the power for the fuse panel.
See where the tunnel slopes up to the firewall? There's a flat place there. That's where I put mine.
 

RED LS1

SENIOR MEMBER
Yes you did. They were helpful but they weren't geared towards where the hole in the firewall was placed. I'm not saying I'm about to drill a hole in the same spot but I figured since I have the firewall bare i'd ask you to be more specific. Is there any reason you didn't go back through the original cabin hole and down the passenger side instead of through the center?


I know the fuse block bulkhead separates into 2 different harnesses. I have the engine harness out now. What did you do there? Did you cut the necessary wires from the engine harness to keep what was needed? I talked to Caspers a little while back and he said he could make me a new plug in that only retained the needed wires there .
 

Chuck Leeper

Toxic old bastard
Staff member
O
Yes you did. They were helpful but they weren't geared towards where the hole in the firewall was placed. I'm not saying I'm about to drill a hole in the same spot but I figured since I have the firewall bare i'd ask you to be more specific. Is there any reason you didn't go back through the original cabin hole and down the passenger side instead of through the center?


I know the fuse block bulkhead separates into 2 different harnesses. I have the engine harness out now. What did you do there? Did you cut the necessary wires from the engine harness to keep what was needed? I talked to Caspers a little while back and he said he could make me a new plug in that only retained the needed wires there .
I depinned the unnecessary wires. Nothing was cut. You can remove the locks and then pull the wires out. No cutting necessary.
Caspers is a nice piece. If you don't want to mess w/ the old stuff, that's the way I'd go.
If you look at the pics, there are 2 that clearly show where the harness goes thru the f wall. one from each side of the wall.
I ran it that way because I didn't want the harness draped over the engine from the pass side. This is a turbo app and there's way too much heat there to expose a harness to. [4" d/p].
 

Tyler Stipe

New Member
O

I depinned the unnecessary wires. Nothing was cut. You can remove the locks and then pull the wires out. No cutting necessary.
Caspers is a nice piece. If you don't want to mess w/ the old stuff, that's the way I'd go.
If you look at the pics, there are 2 that clearly show where the harness goes thru the f wall. one from each side of the wall.
I ran it that way because I didn't want the harness draped over the engine from the pass side. This is a turbo app and there's way too much heat there to expose a harness to. [4" d/p].
I know this is an old thread but I’m changing the routing of my Holley harness; is the flat horizontal part where you put the hole in the firewall? And what size hole did you make? Thinking about 2 1/8”.

Thanks! View attachment
 

Chuck Leeper

Toxic old bastard
Staff member
You can go there with the harness. That will put it in line with the engine.
We also use these pieces that we have laser cut.
It allows for a larger hole and yet retains the grommet.
 

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