Top 5 LS Swap Add-Ons From Speartech Fuel Injection Systems

When it comes to cramming a GM LS or LT motor into a vehicle that was never intended to be propelled by a modern V8, certain “amenities” must be made along the way. Reformed firewalls, chopped-up crossmembers, tweaked transmission tunnels, and reimagined radiator relocation options become mandatory modifications more times than not, especially when the chassis in question is a car that was never designed to be powered by an LS or LT motor with bolt-ons. But restomod swaps aren’t all grinding wheels, Sawzall shenanigans, and wacky welding points, either. 

The electronic end of the average LS and LT conversion requires just as much creativity and customization as the metal fabrication side of the equation. Figuring out how to get all of those wires, switches, modules, and pigtails installed and functioning correctly can be quite an intimidating undertaking, especially when working with an older chassis that was never meant to sport such modern amenities. Fortunately, the GM V8 swaps of today no longer require an electrical engineering degree or nearly as much prayer as they once did, thanks to companies like Indiana-based Speartech Fuel Injection Systems, Inc.  

In-house assembly and testing are but one of the many additional perks enthusiasts benefit from when purchasing a Speartech wiring solution.

While owner and operator, John Spears, has made a name for himself by constructing one-off LS and LT electrical conversion solutions for well over 20 years, the Speartech brand offers much more than engine wiring harnesses and transmission control systems. Speartech has developed some clever solutions for GM enthusiasts who are on the hunt for plug-and-play swap solutions and those who desire a more all-encompassing LS or LT upgrade. Today, we’ll discuss what electronic options, performance perks, and Speartech exclusive solutions are offered for restomod GM aficionado and beginner builders alike.

The Speartech Story

Heralded as the home of the original LS swap harness, Speartech and its founder, John Spears, have single-handedly reimagined what the GM V8 conversion can accomplish. Thanks to this man’s irrepressible passion for LS and LT swapped vehicles, each passing year brings with it easier, more reliable, and all-encompassing swap options. From standalone swap harnesses and complete control systems for modern LS and LT engines and transmissions to 6L80/90, 8L90, and 10L90 conversion accessories and in-house assembly and testing, Speartech takes the time to do it all.

Long before John Spears was an LS and LT engine swap mastermind, he earned his bread as an electrical systems engineer for General Motors. During that 23 year stint with the Detroit-based brand, a massive portion of Spears’ focus became acutely focused on all things related to engine control and ignition system development.

Although your powertrain swap will go in and operate properly, giving you years of exciting, trouble-free performance, Speartech offers several options that can be installed that will enhance the performance, enjoyment, and safety of your vehicle. – John Spears 

Eventually, Spears’ job assignments led him to work in the Delphi engine dynamometer development center, where he helped “spearhead” many ignition systems utilized in today’s GM vehicles. Around this time, Spears also began working on a project that focused on improving engine computer calibrations for quick starts in cold weather, which eventually led him to be a key player in developing PCM and ignition system interfaces. Naturally, these assignments and subsequent successes caused John to develop a deep affinity for all things electronically fuel injected and engine and transmission control related operations. 

Speartech’s all-encompassing product line proves that completing an LS or LT swap in an older chassis goes well beyond a clean engine bay and boatloads of torque.

Despite being more than a decade ahead of the whole “LS Craze,” John Spears saw the direction that the aftermarket community was headed. So after more than 20 years with General Motors, the electrical mastermind turned in his keycard and set out to start what would become Speartech Fuel Injection Systems, Inc.

Looking Beyond the Harness

GM engineering street cred established, John Spears turned toward the task of taking his engineering expertise and electrical craftsmanship and applying it to every product he could come up with for stuffing LS motors into retro GM vehicles. At the time, plug-and-play options were virtually non-existent for conversions of this caliber, and Speartech soon found itself leading the fuel-injected V8 swap charge.

Here’s a look at a Gen IV harness from Speartech. And while this is a big piece of the puzzle, the company offers a lot of accessories to make your LS or LT swap complete.

Naturally, it didn’t take long before Spears’ acute attention to detail and ability to turn LS swaps into a straightforward wiring affair caused Speartech Fuel Injection Systems, Inc. to become revered as a top-tier electrical solution center, with conversion wiring harnesses being the company’s primary focus.

However, there’s way more to swapping in a modern GM V8 than ordering a one-off wiring harness and hooking it up. Small stuff, like extended O2 socket pigtails, transmission control modules, and reverse light switches, are a few of the many components that many people fail to consider, but not John Spears.

Speartech’s accessory line proves that ordering a simple conversion harness and a transmission control module is little more than a double serving of the massive GM American V8 pie. To make a swap feel complete and perform properly, items like integrated cruise control steering column stalks, gear selection indicators, neutral/parking safety switches, “tap shifter” boxes, and floor-mounted tap shifters must all be assembled and installed.

Not sure how these parts play a role in the construction of a GM restomod build? Here are a few examples to show you precisely how a Speartech accessory line can make an LS or LT swap feel complete and function flawlessly for decades to come.

Neutralize Yourself

Take Speartech’s neutral/parking safety switches, for instance. These often overlooked yet undeniably vital pieces of engine engagement equipment are a royal pain in the patella to deal with, even for those who are familiar with transmission swaps and electrical work. Speartech’s neutral/parking switch modules allow you to skip all of the starter stress. This is achieved via the interception of signal data from the CAN-bus and then manipulation. It only engages the starter when the vehicle is in park or neutral and requires little more than affixing a single wire to the vehicle’s ignition switch “start/crank” wire.

Speartech’s neutral/parking safety switch is one of many parts that must be included in order to get a modern GM V8 to function in an older automobile.

All of Speartech’s neutral safety switch (NSS) modules for 6L80/6L90/8L90 transmissions come with an instruction sheet, quick disconnect pigtails, and clearly labeled wiring for error-free installation. Just note that these modules are not compatible with GM Performance Parts Connect & Cruise packages.

Cruisin’ for a Reason

As for the cruise control side of the scenario, Speartech tackles the issue of older vehicles not having this option by giving Gen 4 swap owners with an E38 engine control module (ECM) and Gen 5 swap setups sporting the E92 ECM, a harness integrated solution that is truly plug-and-play. For those who already have a harness, Speartech’s cruise control kit can be ordered as an add-on, with easy-to-follow instructions and clearly labeled wiring, making install a walk in the park. Just choose your cruise switch style, and let Speartech know what type of throttle pedal you’ll be using, and it will handle the rest. However, note that these cruise control kits do not work with General Motors harnesses, so bear that in mind before buying.

Get Your Rear in Gear

Taking a wild guess at what gear you’re in before shifting is kind of like going to the toilet in the dark. There’s an excellent chance you’ll emerge triumphantly, but things can get messy quickly if you miss your mark. However, if you have a Speartech gear indicator on deck, you’ll never have to worry about missing a shift while rowing through a 6L80, 6L90, or 8L90 transmission. 

These vibrantly colored numerical indicators required to function are a quick plop into your OBD-II port or a tie-in to a Speartech harness that’s still under construction, and you are good to row. This simple yet super practical modern tech add-on lets you see what gear you’re in when tap-shifting easily and can be purchased in red, blue, green, and yellow options. Each indicator measures 2–inches tall, 1.25–inches wide, and 1/2–inch thick and comes covered under a 12–month warranty from the date of purchase. Just note that if you plan on doing any tuning, disconnecting the gear indicator will be required.

I’d Tap That

Another solid add-on option that Speartech developed is its series of “tap-shift” options and inline relays. Designed for those looking for complete control of their transmission, this solution gives automatic transmission owners endless hours of shifting enjoyment without all of the headaches associated with a manual clutch. There’s even a floor-mounted, 8L90 option for those looking to tackle gear selection via Speartech’s modified tap shifter. Just note that this product requires an 8L90 Tap Shift CAN Relay to work on Gen 5 swaps rocking the 8L90 transmission, and it will not work with GMPP computers.

A complete Speartech tap shifter assembly, pictured with CAN reverse light control module and bracketry.

Each kit includes the required shifter cable and necessary mounting brackets and measures around 57–inches in length. For more details on this unique shifter solution, contact Speartech directly, as it will need to discuss things like ECM calibration needs and whatnot before proceeding.

A close look at the wiring, switch, pigtail socket, and control module that go into making a Speartech “tap shifter” work.

Additional Odds, And Ends 

Other standouts in the Speartech lineup include LS injector pigtails, which come ready to solder to an existing harness, O2 sensor extensions, and a tricked-out LS air intake system complete with LS3/LS7 MAF bung, K&N air filter, and PCV air inlet hardware. This intake can be adapted to fit on either the passenger or driver side, and for an extra fee, can be outfitted with an LS3/LS7 MAF sensor for a complete bolt-in solution. There’s also an ETC Pedal to Module Harness, an OBD2 Dual Outlet Port for those in need of an extra scanning/data logging option, as well as a 4–pin to 2–pin alternator connector that allows you to combine LS1 and LS2 electrical charging power easily. 

While all of these, and many more, clever swap add-ons can be ordered at any time from Speartech’s website, there is something to be said for those who do their research and plan things out in advance. Including any of the swap accessories along with your custom wiring harness order will help guarantee that everything is fully integrated and certified to function with every other component on the vehicle. 

In addition, Spears and his team take the time and test every product they make in-house before sending it out the door for a completely painless plug-and-play swap scenario that is sure to function without issue for the lifespan of the vehicle. For more information on Speartech and a list of all of their innovative products, be sure to visit

Article Sources

About the author

Micah Wright

Raised on LEGOs by grandfathers who insisted on fixing everything themselves, Micah has been a petrolhead in training since age four. His favorite past times include craft beer, strong cigars, fast cars, and culinary creativity in all of its forms.
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