Upgrading to LS technology is a no brainer, but staring down a wiring harness can be a little intimidating. We worked with the team at Current Performance – one of the leaders in LSX Wiring Conversions, to help create this guide that will help you swap an LSX family engine into just about anything.

We’ve all read the magazine articles and seen the cars at the local cruise-in events. Those shiny modern LS based engine in an old hot rod, classic truck, or even mid 80’s late model sleeper. The concept is as classic as hot rodding itself and harkens back to the days of throwing a flat head Ford in that old Model A behind the barn or slamming a Oldsmobile Rocket V8 into some left over post-war iron. The concept hasn’t changed but the means of implementation certainly have.

The trend these days is modern fuel injection engines and the wonderful cold start characteristics, the beautiful drivability, and the efficient fuel economy that no carburetor could ever replicate. Couple this with the latest computer controlled overdrive automatic or manual transmission and you can achieve modern performance with classic car looks. While most hot rodders can tackle the basic hardware installation of the engine into their chassis, the wiring systems and computer systems needed to run these modern engines is the most daunting task to making all of this work.

This article is going to tell you what you need to know when starting an LSX engine swap. We’re going to overview everything from the theory behind wiring harnesses, to practical tips and tricks that will help you do the conversion in your garage.

Here’s what this article will include:

• Overview of Current Performance
• Basics to LSX Wiring Conversions
• Differences between LSX Engine Family Wiring Requirements
• Guide to Current Performance Wiring Kits
• Information on Computers & Control Systems

Let’s get started talking a little bit about Current Performance:

A company that has made a name for itself in the retrofit wire harness market is Current Performance out of Hudson, FL. Jared Ochs, the owner of Current Performance, started out working for various shops that completed V8 swaps into late model S10 pickup trucks. His specialty is working through all of the wiring diagram pinouts and developing plug and play retrofits for S10 pickups. The skills honed on those packages allowed Jared to start Current Performance and build complete retrofit wiring harness for custom vehicle applications. Complete and custom are two words that Jared likes to use to describe his harnesses. Each harness is built to the individual customers needs and will have the needed hook ups to integrate the harness into the vehicle wiring.

Check out a snap shop of his web site below:

Current Performance harness’s includes all of the needed fuses and relays and uses OEM type TXL wire for factory like durability. The harnesses are simplified down to separate one wire hook ups for battery power, key on power, fuel pump power, check engine light, and even the cranking or starter circuits. Jared will even supply any needed sensors and a PCM (new or remanufactured depending on year) that is flashed with the correct software program for your engine and ready to run. Current will set up the computer for the transmission, axle and tire size used in the vehicle so that it will shift correctly and will accurately know the vehicle speed. Current will also set the computer up so all of the pesky emissions sensors that are not needed don’t set off false check engine lights.

Picking Your Engine

The key to wiring an LSX engine is knowing what you have, and getting what you need, I know that sounds like common sense, but it’s not as simple as it sounds. There are literally dozens of different LS engine types and designation, many of which use different sensors to do the same thing. If the computer and wiring are not properly matched to the engine and hardware your using, plan on loosing some hair during the debugging process. Once you figure it out, there is a good chance it will be very difficult and or expensive to fix. So unless you don’t care about your hair or your wallet, be sure to do your homework and figure out what you have for an engine before figuring out your control system.

LS1/LS2

The first task is getting the correct engine and identifying it so it can be matched with the correct computer and wiring harness. For this discussion, we will focus on the LS1 and LS2 based engines coupled to a 4 speed automatic overdrive transmission or 5 or 6 speed manual transmission. The LS1 based engines were found in 1997-2004 Corvette, 1998-2004 Camaro and 2004 GTO in 5.7L displacement.

The LS based truck engines were found in 1999-2006 pickups, Tahoe, Suburban and heavy duty trucks with 4.8L, 5.3L, 6.0L and 6.0L high output configurations. From a wiring and controls system standpoint, all of these engines will use the same basic wiring harness and Powertrain control module (PCM). The calibration or software program in the PCM will change depending on the displacement of the engine.

A current performance complete LS2 Engine kit for LS2/LS7 58 tooth engine shown Includes Engine harness, pre-programmed computer, and Accelerator Pedal.

24 tooth vs. 58 tooth trigger wheels

The LS1 engines use a 24 tooth crank trigger wheel. The LS1 engines can also be identified because the camshaft position sensor is located behind the intake manifold at the bell housing flange.

LS2 Engines

The LS2 based engines are the next larger family that went through a mid cycle change that can really cause headaches to the hot rodders retrofitting them.

The LS2 engine came with both a 24 tooth (24x) crank trigger wheel and a 58 tooth (58x) crank trigger wheel. The LS2 engines are easily identified because the camshaft position sensor was relocated to the front timing cover of the engine.

LS2 engines throw curve balls into the ease of parts swapping. They were primarily 6.0L variants and available in 2005-2006 GTO, 2005-2007 Corvette, Trailblazer SS and Cadillac CTS-V. However 24x variants were only used in 2005 Corvette, and most (but not all) 2005 GTOs. To determine the variant you have, the best way is to inspect the crank sensor color. This sensor is located behind the starter which makes in vehicle inspection tricky but not impossible. Black sensors are for 24x trigger wheels while Gray sensors are for 58x trigger wheels. This is important, because you will need to know it later when purchasing a wiring harness and computer.

2007 Truck Engines

The last big engine family variation is the 2007+ truck based engines and front wheel drive Impala. While these engines are based more closely on 58x LS2 engines, they usually include features like displacement on demand and variable cam timing. These engines were sold as 5.3L, 6.0L, and 6.2L variants. It is possible to retrofit these engines but the added complexity of those systems along with unique transmission choices makes these engines less than ideal for first time retrofitters. Working with your wire harness manufacturer to understand the systems will cover most issues with integrating those engines into an older chassis.

For transmission choices, the plans are much simpler. The classic and popular 4L60e will handle most stock engine retrofits. The popularity of this transmission has allowed many high performance parts to become available for increased torque capacity or you can get it built in with the 4L65e that was found in full size trucks with the optional towing package. If your engine uses a 58x crank trigger, your only option is a 4L70 transmission. This transmission was used in GTO, Trailblazer SS, and 07+ full size truck and is unique in that it has an input shaft speed sensor. The 4L70 transmission has a slightly higher torque capacity than a 4L60 but the added input shaft speed sensor is a must have for compatibility with any 58x PCM.

There are some additional hardware considerations to make, which will have huge impacts on your wiring plans. First, to MAF or not to MAF? All LS1 and LS2 engines utilize a mass air flow sensor or MAF and it is really hard to beat the fuel controlling capabilities of a MAF. The restriction in airflow is minor as compared to the precise fuel control that the sensor allows. It knows exactly how much air is flowing into the engine. Not only does it know the volume of air but it also knows the weight of air in pounds or grams. This allows the engine to compensate for humidity, temperature, and altitude better than any carburetor jetting chart that you would find at the dragstrip. Even thought there are advantages to using a MAF, they can be eliminated to avoid the packaging. Eliminating it does mean some special computer programming and less wiring.

Electronic throttle or drive by wire systems are another option to consider. Why bother with holes in the firewall, throttle cable brackets, linkages and all the adjustments needed to make a cable throttle work. Bolt a pedal assembly to the firewall and plug the connector into the pedal and into the throttle body. GM’s drive by wire system is just as responsive as a cable throttle and helps to remove clutter from the engine bay and firewall. With electronic throttle, cruise control can even be hooked up for added modern convinces, without an additional module.

Things such as cooling fan control (based on coolant temp and vehicle speed), AC clutch control (to turn on the coolant fan for low speed ac performance, idle rpm bump for the extra load), and fuel pump control. The list of possibilities can be endless and extends as far as what that engine had to do in its original chassis. Depending on your project, you may or may not have or need antilock brakes, air bags, or fuel vapor purge valves. The key is to figure out what you have, want and need before taking the next steps.

Wires and more Wires

Now that we have an idea what engine and hardware we have we have to figure out how to wire everything up. This can be a daunting task to the experienced and inexperienced alike. A modern vehicle harness can contain well over 2000 circuits with only about 1/10th of those needed to make one LS engine run by itself. On top of that, knowing for sure what circuits to keep and what to remove leaves the harness in a state of experimentation. Until you plug everything in and try to run the engine, then you will know for sure if you removed more than you needed. Sure you can get the entire wiring harness and start modifying. The vast majority of people are more qualified to perform surgery, than to take on a task like modifying a wiring harness.

Current Performance has the solutions

With all the options and possibilities, there is no magic bullet wiring harness’ which is where Current Performance steps in with different products to fit virtually every need.

Custom Built Wiring Harness

Adding a late model powertrain to a late model vehicle is the perfect fit for a custom harness. By matching the engine options with the vehicle, Current Performance custom builds a harness which allows the engine to communicate with all of the complex vehicle electronics. That means swapping a V8 into a Colorado pick-up, Pontiac Solstice, or maybe that upgrade to your V6 F-body, can be plug and play with one of these harness’ from Current Performance.

Stand Alone Wiring Harness

Adding an LS engine to a Hot Rod requires a few simple connections to things like power and ground. With this option, Current Performance supplies just the basics to make the engine sensors work with the computer but have very little integration to the vehicles electronics. That means things like gauges need to be handled independently.

Example of a Current Performane GTO LS2 harness modified to stand alone.

Modification of Factory Harness

This is sort of the junk yard special budget option. If you get your engine complete with harness, Current Performance will use it as the building block of a custom harness for your application. That means leaving the hardest part to the experts, it’s kind of like leaving the surgery to the doctors.

We asked Jarod what advantages of a custom built harness verse a modified harness “with the used harness, they are limited to where the computer is going to mount by the length of that harness. Also, if it has been cut, or damaged, it may be better to go with a new harness. So basically, if they are happy with where they are going to have to put the computer, and the original harness appears to be in good shape, then save your money and just re-use the original wiring. One other advantage to a new harness, especially on the truck engines, is that we route them differently and it just looks a lot cleaner on the engine.”

Current perforamnce can custom build harness’ for transplant vehicles like this LS-2 powered Chevy Colorado

Computers and Control Systems

Now that we know what engine we have, and the harness, its time to pick brain in this case a computer which will make all of the fuel injectors, coils, and sensors do their thing? With all of the various computers and controllers out there for custom fuel injection engines and race cars, it is hard to compete with the stock computer (and software inside) that GM has used on thousands of vehicles on the road all over the world. The decision for what computer really comes down to what the end product will be. A race car engine deserves a race car computer system which isn’t really the point of this article. However most of the retrofit transplants that are done utilize a stock engine or bolt on modifications that would be equivalently done to the donor vehicle.

If I had a late model Corvette, and did a mild heads and cam swap, the intent of that vehicle would be to use the stock computer system. In the end, it is hard to compete with the power of the stock computer. The power doesn’t come from the speed of the computer but the complexity of the software inside that computer. GM has spent millions upon millions of dollars developing software control systems to handle everything you can do to that engine.

If the engine runs too hot, it will automatically reduce spark. If you are limited by your octane choice at a fuel pump in the middle of cruise through New Mexico, the knock sensors will pull back spark and prevent detonation. The computer is smart enough to see that the engine is running a little lean and will richen it up and learn that value for the next time you drive the vehicle. The added benefits of the stock PCM is that it has so many factory inputs and outputs to aid in turning the classic car to a modern street machine.

Purchasing a GM computer is like buying a key, it may look like it’s right, but chances are it will not work. It’s simple, when you need a key, you tell your lock smith what you need and he sells you the correct part. When you have everything figured out, buy the matching computer from a professional like Current Performance who knows the correct part number for your combo. If you are running a stock engine, the correct tune can be installed prior to shipment. If you have done some customizing, you may need a custom calibration or “tune” which pulls it all together

The Next Steps

This is where the bench racing and garage dreaming ends and the real work begins. When the engine, wiring harness, and PCM are sitting in the garage and ready to drop into that chassis, the next steps come into play and the actual hardware fitment starts. Engine mounts, exhaust, gauge sensor hook ups, plumbing adapters, and water hoses are just a brief sampling of the hardware and parts that will be needed to complete everything. In a future article, we will follow more step by step into the nuts and bolts of an LS engine retrofit. Now start calling the junk yards and continue the traditions of our hot rodding fore fathers to get a modern high performance engine to that project car.