Complete Your LS Swap With A Standalone Wiring Harness

In a series on LS engine swaps we can’t leave out the need to wire it up! Your ‘69 Camaro, ‘70s Chevelle, or even ‘90s Firebird isn’t set up to run an LS engine—so, you need to get your hands on a wiring harness to run that thing. Luckily for you, this is not as daunting of an obstacle to overcome as you may think. In fact, getting that LS to run can be a breeze.

What are my options for running an LS engine?

You have two options to getting your LS to run: either you get a standalone harness or you get yourself set up with a carburetor. Yeah, a carburetor. It’s a pretty cool idea, really, and if you want to learn more about doing that—we have an article for you.

But let’s say you’re sticking to fuel injection. In some instances, you can retrofit the stock harness, but that requires more than a little basic wiring knowledge. Another option? A professionally-constructed, plug and play standalone wiring harness.

What is a standalone harness?

You may be wondering what in the world standalone means. A standalone harness is used just for engine control, i.e. the basics. Compared to a factory wiring harness, a standalone harness is a bit smaller and features less connections. This is because it is not intended to run a lot of the additional options, like cruise control or fuel management.

That being said, while some standalones feature as little as four connections to get the engine running (say, one each for the battery, ground, ignition, and fuel pump), other connections will need to be made to the computer, sensors for data logging, and so on.

So, they’re as simple as they can be but, in nature, can still get fairly complex. Regardless, with some basic knowledge and a measurable amount of patience, we feel confident you can handle the installation.

What if I want/need those additional options?

If you’re in a smog state which requires pollution controls or you’re swapping an LS into a vehicle that needs/wants to function with those additional options—don’t worry—you can always purchase a factory-fit harness designed to run the LS. Keep in mind that the make and model will determine the manufacturer needed for this.

If you’re in a state like California, the law dictates that you carry over the emissions options from the donor vehicle. Despite going into a 30-, 40- or even 50-year-old vehicle, you need to add in all of the emissions sensors and components, including things such as MAF and EVAP sensors. You may be wondering if a standalone harness is a viable option here. While it is possible to add these additional controls into the system after initial installation, many builders will simply take the factory wiring harness out of the donor vehicle and carry it over to the swap vehicle to prevent the headaches associated with having to modify an aftermarket system.

Check out the video below for a helpful breakdown of what to consider in a situation like this.

Get the Right Stuff

The greater majority of LS swaps will use a standalone harness because they are simple and affordable. Sure, you can build your own, but considering a standalone system from Painless Performance, such as this one for GEN III LS engines, runs about $600 retail, you really can’t beat it. Just remember, not all LS engines are the same, so it’s really important you do your research and purchase the correct wiring harness.

Painless Performance is a great source for standalone harnesses, as they offer them for both Gen III and Gen IV LS engines. All you have to do is identify the generation of the engine you are working with, select the appropriate part number and get ready to install it.

Each Painless Performance harness is quality-tested before it leaves the building to ensure all circuits are viable. Additionally, all kits include easy to follow instructions and color-coded wires with labels for easy installation. Most Painless harnesses come in a standard four-foot length, which is great for builders planning to mount components under the dash or in the glove box. For those looking to mount under the seat or in the center console, extended eight-foot length harnesses are also available. Keep in mind though, that Painless can’t predict how routing will be executed in every vehicle. That means, you’ll need to do some homework.

Plan, Plan, Plan…

Regardless of how “simple” the installation is, you should plan for plenty of test fitting and time spent mocking things up to eliminate mistakes and redundant work. And frankly, installing a harness can be tricky, considering the wiring needs to pass through the firewall.

Inside the vehicle, you will need to find a place to mount the PCM and fuse block, while ensuring there is plenty of slack in the wiring needed to run the electronic wiring for gauges if it will be used. Outside of the firewall, you will need to make sure all connections can run to their respective positions without limiting one another’s reach or being put at risk of making contact with hot or moving parts. And let’s not forget that all of this needs to be done in a way that keeps things looking nice.

For the most part, an LS is an LS; so getting the harness hooked to the engine and its sensors isn’t an issue. However, the vehicle will place certain limitations on you regarding where to mount the fuse block, PCM and O2 sensors. That requires some extra finesse—and planning. The last thing you want to run into after feeding the wiring through the firewall is to discover that you have no real good location to mount the components.

Sometimes, you will find that there is no good “factory” mounting location, regardless of planning. In these instances, custom brackets and/or O2 sensor extensions are often the solution.

Wiring Made Easy

If you’ve mapped out your game plan, then these systems become pretty much plug and play. Still, wiring can be a drag to deal with as it constantly binds on itself. So, work slowly and stay organized. Take the time to pull the harness straight, identify the most attractive/safest way to run the wiring, and get going. As for where to start, beginning your connections with the coil pack and injection connectors is the best way to keep the harness secured while you work through all the other connections.

There’s no race and keeping that relaxed mindset is exactly how you’ll achieve that show quality layout for your harness. For many, knowing which connector will go where is intuitive. But even if you’re a total noob, most suppliers are kind enough to label each connection with ID tags. Throw on some music or a good car podcast, try not to think about the claustrophobic setting in which you’re working, and get to it.

It’s easy to damage a wire when working in such a tight spot. Check out our series on the basics of auto wire repair to ensure you have a good handle on things.

Get the PCM

Remember: You still need a custom tuned PCM to get that LS running. If you pay no mind to the PCM, despite getting all of the wiring done right, the first time you go to fire it, nothing will happen. Obviously, this can be extremely frustrating.

Many times, this problem is because the factory VATS was never disabled. Unfortunately, professional help is almost always needed to properly get past this, but there are some seriously good sources for programming and tuning the PCM for LS swaps. I definitely recommend giving LT1swap.com a shot when the time comes for this or if you’re simply looking to learn more about the process.