What You Need To Know Before Ordering A Standalone Harness

Before you get online and order a new harness for your LS-swap project, there are a few things that you need to know ahead of pulling the trigger on a purchase. In this article, we will look at what you need to know before even thinking about hitting that elusive “Buy Now” button. 

First Things First

It’s always a good idea to know the year, make, and model of the vehicle that your engine came from. Not only will this knowledge help you with ordering a harness, but it will also help when you need parts from the parts store. But if you’re not sure what donor vehicle the engine came from, you can still figure out what harness you need with some research. 

Drive-By-Cable or Drive-By-Wire

As you probably know, the LS engines were available with two different throttle bodies. The first throttle body we will talk about is a drive-by-cable (DBC). These mechanical units were offered in most early model LS engines and used a cable attached to the gas pedal to operate the opening and closing of the throttle body manually. The second type of throttle body is the drive-by-wire (DBW). The DBW unit has a motor in the throttle body controlled by an electronic pedal through the ECU. Each of these assemblies has its pros and cons, but since that’s not the focus of this article, we will move on. 

The drive-by-cable throttle body on the left is typical among the early Gen III LS engines. However, some of the later Gen IIIs came with drive-by-wire units like the one on the right. Images courtesy of Summit Racing and Amazon.

When ordering a harness, you will undoubtedly need to know which throttle body you have. As you can imagine, since the DBW units are electronic, this feature adds a lot more complexity to the harness since it needs to be tied back into the ECU and throttle pedal. With a DBC throttle body, you will need to hook up a cable to the linkage. This is a simple process on older vehicles since most of them utilized mechanical linkage for carburetors and early fuel injection. 

If you have a DBW set up and want to run a DBC instead, you can accomplish that pretty easily by installing a mechanical throttle body. The only issue here is that some factory intake manifolds didn’t have provisions for a cable mount, depending on the intake manifold. So you can either make your own or run an aftermarket intake manifold setup for a DBC throttle body.

Here is a look at some of the DBW GM used over the years. Images courtesy of Speartech, Summit, and Amazon.

GM offered four different types of DBW throttle bodies to complicate the harness selection process. The first one introduced was on the Gen III C5 Corvette from 1997-2004 which features a six-plus two-pin design on the LS6 engine. In 2001-02 a Gen III truck throttle body was introduced with the same pin configuration as the LS6 throttle body. However, a new style was released for the Vortec engine in 2003 that carried on until 2007 with an eight-pin design. The LS2 engine came with a six-pin connector that was available from 2005-06 which is the same connector for the LS3 throttle body. 

Gen III Vs. Gen IV

While these Gen III or Gen IV engines are very similar in design, the sensors used are different, as well as their locations. Another detail that is critical to get correct is the crankshaft reluctor wheel. This wheel is responsible for locating the crank as it spins 360-degrees. A Gen III engine uses a 24-tooth wheel, while a Gen IV can utilize a 24-tooth design in early models or 58-tooth design. If you need some help deciding which generation engine you have, this article from Holley will point you in the right direction. 

Here is a good look at the reluctor wheel on an LS crank. Gen III engines use a 24x wheel with a black crank sensor while 58x versions require a grey body color sensor. Image courtesy of Holley.

Transmissions

The next important thing that you will need to know is what transmission you are planning on using. If you want to run a manual or a non-electronic unit like a Powerglide, TH350, or TH400, the ECU will not need to support the transmission. This modification means there will be a lot less wiring in the harness, which cuts down on the prices and complexity of the installation.

If you are planning on running an electronic transmission behind your LS engine, it helps to know which one you have. The 4L60e, 4L80e, and 6L80e transmissions have different plugs that are not interchangeable. And while companies like BP Automotive offer an adapter in some cases, it’s better to order a harness with the correct adapter. 

Injectors

Here’s where things get a little more complicated. Over the years, GM used several different types of injectors. Fortunately, they’re not hard to identify since they have various styles of plugs and look different. However, if you’re still not sure, you can always get the number off the side of one and do a quick google search. Images like the one below on BP Automotive’s site are a great resource as well. For the Gen III series engines, GM used an EV1, Multech, and EV6. The EV6 was the only injector used on the Gen IV engine. 

Alternator Connection

If you haven’t noticed yet, GM likes to make changes to its engine components at any time. And while we’re sure they have a good reason, we don’t know what prompts these changes. So, it comes as no surprise that the company also uses a couple of different alternator styles, which you will need to address before ordering a standalone harness. Fortunately, there are only two that were used, a four-cavity and a two-cavity design. To identify the correct plug, you will need to look at the alternator and see if it has four or two pins. 

MAF Sensor

The mass airflow sensor (MAF) is another important tuning tool used by the ECU in both the Gen III and Gen IV LS engines. The one used on an LS1 offered aluminum ends which sandwiched a three-pin sensor. The LS2, LS6, and Vortec engines all utilized a one-piece five-wire design. In 2007 GM ditched this design and opted for a different five-wire unit for the 07-08 Vortech and Holden engines. More changes came with the LS3 and LS7 as they were a card-style MAF instead of the traditional round one. In 2009 Chevrolet broke the mold again for the Vortec and CTS-V LSA engines with another new five-wire MAF. To add to the confusion, the MAF for the Express Van from 2003-2013 is also specific to the vehicle but some of the early model Gen III van engines came with the Vortec five-wire MAF.

MAP Sensor

GM also used two types of manifold absolute pressure (MAP) sensors. These parts are easily identified because they are pretty different visually. The somewhat tubby Delphi MAP sensor snaps onto the intake manifold while the Bosch sensor has a hole where a bolt passes through, securing it to the manifold. These units utilize a different plug, so be sure and identify the one you have before ordering a harness. 

Variable Valve Timing (VVT)

Variable valve timing (VVT) was not offered on the GEN III LS engines. However, it was an option on some Gen IV models but not all of them. Fortunately, even though the covers look similar, it’s relatively easy to identify if the engine is equipped with VVT, especially if the water pump is off the engine. If you’re looking at the engine from the front, a Gen IV will have a cam sensor on the right side of the cover. If it’s equipped with VVT, it also has a short harness that will plug into the camshaft phase actuator, also called a timing solenoid on the left. 

Programming

Many aftermarket companies that specialize in building standalone harnesses will offer a tune for stock vehicles or startups. If the engine is stock, you can start the car up and drive it after the installation. You will need to supply some added information about the combination. Things like the rear end gear ratio and tire size will make sure your speedo is accurate and that you won’t have to visit a tuner for any changes. If your engine is modified, you will need to work with a tuner to get the vehicle running properly. 

While this article should help you identify the generation of LS you have and all of the components associated with it, companies like BP Automotive, Speartech, ICT Billet, Holley, and PSI offer a lot more information on their websites. If you still have some questions, you can reach out to a company that builds custom harnesses, and they will be able to walk you through the process as needed.

 

More Sources

About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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