Getting An LS Engine Wired With Howell EFI

When restoring cars, most of us are able to tackle just about any aspect. Things like paint, rebuilding transmissions, or maybe welding are some areas that might be lacking. One area that most of us lack is the knowledge of Electronic Fuel Injection (EFI) wiring. Most hobbyists know the basics of wiring, but EFI harnesses are another level. With a host of new sensors, fuel injectors and other wires, EFI can be intimidating. 

Howell EFI’s manufacturing and office located in Marine City, MI.

One company that decided to tackle this wiring problem head on was Howell Engine Developments. Started by Bill and Matt Howell, they are no stranger to engines. Bill is retired from General Motors, and most of his work with GM included engine development on big-blocks that went into Camaros, Novas and Chevelles. Partnering up with his son Matt in January of 1988, they formed Howell Engine Developments.

“The business came about because GM started coming out with electronic fuel injection on everything and there was no easy way to adapt those engines into other vehicles using the factory harness,” said Bill Howell. From its humble beginning in Bill’s garage, they have now expanded into a building thats almost 10,000 sq. ft. with an additional 4,000 sq. ft. in just storage. With more growth also comes more employees. “We have eleven full time employees and four additional employees that build harnesses at home,” said Bill. 

“We cover just about every GM engine, from the 1985 Corvette on up,” continued Howell. They can even handle the throttle body injected motors, since wiring can get complex with those as well. With the popularity of the LS engines, Howell jumped in head first and builds harnesses for every LS combination there is.  

Options For Getting Wired

When ordering up a Howell harness, there is a lot of modifications they can do to a wiring harness. Bill told us that they start by finding out the requirements needed for the motor by the customer. “We ask the customer where they are going to run the car, what the application is, does it have to be emissions legal, does the customer even care if its emission legal, etc.” Howell wants to know everything about the customers motor and modifications so they can build the exact harness to their specifications. This also allows them to properly tune the computer at their facility. 

Laying out each individual wire.

Other options can include electric fans, wiring for the transmission, gear ratios, and tire size. When a customer orders a Howell wiring harness, there is an extensive checklist they fill out in order to get the correct wiring harness for their application. There is no universal “off the shelf” harnesses that requires modification from the customer. All the harnesses are built to customer specs and are ready to be installed.  

Just about every color, gauge and variation of wire is available at Howell.

The harnesses themselves are as close as possible to factory in regards to wire color and terminals. “We have a vast selection of colors and gauges, and we try to match those as close as we can to GM harnesses,” said Howell. That allows you to still use your factory wiring diagram, should you need to know what wire is going where. 

Howell also explained that, “Sometimes the factory uses 22-gauge wiring which we feel is scary small, so we will use a 20 or 18-gauge wire in its place to ensure a quality connection.” They will also upgrade some of the other wires, like the alternator wiring. This usually happens when somebody is running a high performance aftermarket alternator that’s pumping out higher amperage than stock. 

Racks and racks of OEM connectors.

At the ends of the upgraded wiring are quality terminals. “We buy and use the same Delphi terminals that GM uses,” said Howell. “In order to get them, we have to buy them in large quantities, but this also means we have plenty in stock at all times.” These terminals need to be a quality piece, as something of lesser quality could break or become brittle with heat and age. These terminals have been developed over the years by Packard and Delphi divisions of GM for long term durability. 

Assembling connectors by hand.

Another good thing about a new, custom made harness is that Howell can build the harness longer or shorter, so that you can easily hide the computer. Most stock harnesses mount the computer on the fender well. While that’s practical, its not exactly the best looking. Howell has even built some really long harnesses that allowed the user to mount the computer in the trunk out of the way. 

Every harness Howell makes is customized for your application. We asked them why they don’t make a basic “off the shelf” wiring harness. “Every single engine is different with different requirements. There is just too many variations involved to make a single off the shelf wiring harness,” said Howell. With a dozen different LS variations, making something that fits a 4.8-liter naturally aspirated truck engine won’t cross over to a 6.2-liter LS. While the external size of these motors are basically the same, the required sensors, tune and computer location is going to be different for every harness. 

Computers and Tuning

“We only use GM computers, but we do reprogram them,” says Howell. Bill Howell found out that GM computers are really reliable and rarely fail, even coming from a salvage vehicle. “We are still buying computers from cars that were built in the 1980’s, its amazing how few get rejected when we test them,” continued Howell.

There are two options for ordering computers from Howell: the customer can purchase one of their’s or they can reprogram the customers. This is one part of their harnesses that isn’t 100% new, but the computers do get run on a live engine to make sure they are working flawlessly before being sent to the customer where they are guaranteed for a year. 

“We do all of our own tuning in house. This allows us to custom tune every computer for the exact requirements needed on the motor.” – Bill Howell, Howell EFI

When it comes to tuning the computers Howell said that, “We do all of our own tuning in house. This allows us to custom tune every computer for the exact requirements needed on the motor.” Howell also mentioned they have a large library of tunes that they have done over the years that handles most applications. For 95% of the reprogramming they utilize EFI-Live, with remaining tuning done with HP Tuners.

But what if you want to run an aftermarket computer, such as a Holley Dominator ECU? Howell has many different plugs available to handle many aftermarket computers, allowing greater flexibility. 

Factory computers ready to be tuned for your motor!

What To Expect

100% assembled in the USA!

When ordering something 100% custom, most enthusiasts are use to a month to two month wait. That’s not the case with Howell. From the time the customer orders their wiring harness to the time it ships is usually around one week, depending on the season and demand.

When the customer does receive the wiring harness, they might wonder where to start and be intimidated with all the wires and plugs. Howell keeps their support going by labeling every single wire, keeping the guess work out of attaching the harness. If you do get stuck, you can always refer to the installation manual or give them a call and speak with a professional. 

What if you accidentally crush a connector when working on your car? No problems there. Howell sells their connectors individually as well. There is also other wiring products available on the site, from the connectors to ignition coils and everything electrical on the motor.

With over 25 years in the wiring business, Howell can handle just about any requirement you can throw at them. All their harnesses are made in Marine City, MI, only an hour away from Detroit. Remember that they do just about every GM engine from 1985 on, so no matter how you look at it, Howells got you connected! 


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About the author

Tim King

Tim grew up in the garage with his Father. From those early years grew a passion for anything with a motor. Helping his Dad and brother restore a '67 Nova is what fueled Tim’s passion for cars. At the age of 15 he bought his first car, a 1966 Chevelle which he still owns to this day. That car started his journey into the automotive world where he’s done just about everything, from being an auto mechanic to an aftermarket Sales Manager. Not only is he a gear head, but he also holds two Bachelors degrees from Cal State San Bernardino.
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