LS Engine Wiring Guide

Built6spdMCSS

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Jun 15, 2012
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I'm gonna post this up so it may help some people.

Bunch of LS Engine Wiring Harness schematics here:

Here is the diagram for the Gbody Firewall Bulkhead Connector:

Screenshot_20230221-142244_Gallery.jpg


I posted the link for the schematics in reference to what some people may have as "standalone harnesses" or you build your own, can use the schematics to double check what you have.

The wiring on the Firewall Bulkhead is simple:

Two 12ga RED wires are 12v battery wires coming in off the battery POS cable at the starter, they have fuseable links on them. These both go into the ignition switch on the column.

Single 12ga PURPLE wire is from the ignition switch on the column to the starter solonoid to start the car.

Single 12ga PINK wire is the 12v Key-on Ignition wire to the Distributor.

Mentioning them above because they are important. The rest are labeled as such. Leave the lights and horn wiring alone.

EFI LS Swap is simple.

Keep the two RED going into the Firewall powered from battery POS 12v. They do not have to be connected to the starter if you install a fuse box that connects to the battery, and has outputs that are constant battery power. 12v battery outputs on the fuse box can be spliced to these two wires going to the Firewall. Would be wise to have a fuse on them somewhere if the fuse box doesn't.

PURPLE 12ga needs to stay from the Firewall Bulkhead going to the little peg on the starter solonoid.

PINK 12ga wire gets connected into any circuit that needs 12v key-on ignition power.

All the wiring that is connected in the existing SBC/V6 Engine Harness can be clipped and re-purposed since you're installing the LS EFI Harness.

I used that wiring and built several circuits that I needed depending on how I ran wires.

I make it sound simple, there not much to it as long as you understand a wire has two ends. The rest is up to you how you want to do it.

I installed the whole fuse box out of a 1998 Camaro into my SS, spliced in the fuse box into the existing factory Gbody firewall bulkhead wiring. Since it was a GM fuse box all the colors matched. 4ga wire from the battery ties into the fuse box to give it 12v, from there I connected the two RED 12ga wires going into the firewall bulkhead. PINK 12ga coming out connects to the Pink wire on the fuse box 12v key-on Ignition circuits. PURPLE 12ga goes to the Starter through the engine harness. My LS engine harness plugs into the fuse box portion that connects to the wiring for the LS Engine & PCM. I also have a connector inside of the car to run the gauges and to the OBDII DLC.

That's pretty much it. 👍
 
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87National

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Good stuff......between what you posted and your link to lt1swap.com......that completely covers thinning out a factory ls harness and integrating it into a g-body.

How big of a fuse would you place inline with the red wires?
 
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Built6spdMCSS

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Exactly why I posted it, it's that simple when you have the resources in front of you. Just tedious gettin in there.

In my car those big ones are 50A Fuses if I remember right, then again factory 1998 Camaro Fuse Box. Might be able to look up the spec on the factory Gbody fuseable link.
 
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Ribbedroof

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GP403 ...Sticky!

Built6spdMCSS .. Thanks for posting this. Despite the enormous amount of LS swap "stuff" on the web, it's nice to have a clear, concise, breakdown in a single place. Much better than the drama that ensued in the last go-around. Not that my opinion matters, but thanks.
 
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Built6spdMCSS

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Jun 15, 2012
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Good stuff......between what you posted and your link to lt1swap.com......that completely covers thinning out a factory ls harness and integrating it into a g-body.
The one thing I did leave out is anything that is ORANGE wires, none of them are in the Gbody wiring there on the firewall bulkhead.

They are in the factory GM Fuse Boxes, and are FUSED CONSTANT POWER.

Several circuits in the LS wiring that are that type, basically the constant PCM power. Some of these aftermarket "standalone" harnesses are wired correctly for it or specify it, then again it comes down to how you install it all.
 
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Built6spdMCSS

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Jun 15, 2012
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I didn't realize this made it to sticky status.. GP403 I cleaned up that one post a while back, point was delivered so keeping the good technical stuff on point. Good info here for people to use, I'll put out there what I've learned.
 
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Cams85GP

Not-quite-so-new-guy
May 30, 2021
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Ontario Canada
This post helps a lot.
Just a couple things I’m stuck on.

Since I’m running the MSD 6014, the pink 12V key on that was meant for the distributor, can now be wired to the red wire from MSD box?, I’m assuming through a relay as per the instructions?

Also, the single brown wire originally meant for my V6 alternator, can now be spliced into a 1 wire pigtail into new LS alternator, through a resistor I believe.?

Thanks
 

Cams85GP

Not-quite-so-new-guy
May 30, 2021
25
47
13
Ontario Canada
Several ways people have done the alternator.

What is the function of the red wire on the MSD Box?
Instructions say “battery positive. From relay or dedicated fused 30A switch” . The picture is from the instructions.
As far as the alternator goes, that’s why I’m stuck, different videos say different things. I’d like the cleanest and easiest setup.
C079010C-C56C-4C8A-A81A-DE7F2C21D4D7.jpeg
 

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