The wiring aspect of any LS swap is undoubtedly the most difficult. Most builders are familiar with fabrication techniques, trouble shooting, and parts swapping to make things work, but electronics rise to a much higher level of complexity. Wiring has carried an aura of mystery that can send a shiver down the spine of even the most seasoned builder, making them wish for a simple carburetor and distributor. If you fall into this group, don’t lose hope. This chapter has the answers you seek with easy-to-understand instructions for tackling the wiring of an LS swap.
This Tech Tip is from the full book, LS SWAPS: HOW TO SWAP GM LS ENGINES INTO ALMOST ANYTHING. For a comprehensive guide on this entire subject, you can visit this link:
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Retrofitting the stock harness requires knowledge of electrical circuits, soldering skills, and attention to detail. It is not a simple plug-and-play procedure, so make sure you are up to the task before hacking into the wiring harness.
Gen III/IV engines feature complex computers that control everything from timing and ignition to fuel and air intake. On many LS engines, even the throttle is computer controlled; the pedal is connected to a sensor box that tells the throttle how much to open. These systems can be overwhelming, but the key is to tackle one circuit at a time. Although the factory systems are certainly adequate, the aftermarket has fully embraced the LS platform and there is definitely more than one way to do it right.
Wiring Harness Basics
If you picked up an engine from a salvage yard or other used vehicle, you need all the electrical components to go with it. Let me repeat: it is imperative to get everything. This includes the computer, wiring harness, mass airflow sensor (MAF), oxygen sensors, and if the engine is drive-by-wire, the gas pedal and throttle actuator control (TAC) module. Each engine requires the use of its own specific computer and harness, and keep in mind that there were changes made to each system year by year. In order to reuse as many of the factory components as possible, you need to get all of them with the engine. Matching key components such as a TAC module with the ECM can be tricky without all vehicle/engine-specific details such as year, make, and model.
A stock harness can be used asisin the swap, or can be given the “wire diet” by cutting off the loom and removing the wires that are not needed. This is a great way to get to know the engine’s wiring in detail. Keeping track of each wire can be a bit of a headache, though.
Whether using a stock or an aftermarket harness, the cleaner the install, the better. This Painless Performance PowerBraid protects the wires from abrasions and heat while keeping a stock look.
Friction tape at the ends secures the braid. Regular electrical tape works, but make sure it is good-quality stuff such as 3M Super 33. The cheap stuff falls off.
Each Painless Performance kit comes with all the basics: terminal pack, relays, and zip ties. You often need more terminals than what is included, so be sure to have plenty of assorted terminals on hand. Bulk terminals can be ordered directly from Painless.
Here is the completed wire-diet LS1 harness install with the full loom. This takes some time to complete, but the results are worth it.
Retrofitting a stock wiring harnessis seemingly complex and perhaps overwhelming. In fact, it is really not that difficult. With the proper diagrams and instructions, it can be modified to greatly simplify the process of wiring the engine. The majority of the wires in the stock harness are not needed in a retrofit application. Seriously, what 1969 Camaro needs an evaporative canister purge solenoid control? There are differing opinions on what to remove from the stock wiring harness, however.
Wiring a Classic Corvette
Rat’s nest, spaghetti, copper conjunctivitis; call it what you want, but wiring is the single most feared aspect of all automotive projects. Whether you are chasing gremlins through a 50-year-old survivor or rewiring a muscle car, most gearheads just don’t enjoy wiring. It doesn’t have to be this way, though, as there are tricks and tips that can turn a nightmare into a job well done. And it doesn’t require a degree in electrical engineering either.
There are two main types of wiring projects: fixing an existing system or replacing it. With 40-plus-year-old wires, often the best solution is total replacement, especially if the car is apart already.
The crew at Red Dirt Rodz handled all of the wiring details for this 1967 Corvette roadster. This car came into the shop as many do, fully disassembled, as one person’s failed build sold off to another. Although the original harness was still there, most of the terminals were broken, the wires were cracked and corroded, and it simply was not worth trying to fix, especially considering the car was being fully rebuilt. Starting with a clean slate is always nice. One call to Painless Performance and the harness was on its way.
They could have ordered a factory replacement harness, which is already terminated and bundled, just like the factory harness, and every-thing is where it should be for the stock components. But that wouldn’t work for this project as the roadster has an LS1, electronic transmission, aftermarket gauges, and all the new-fangled goodies found on a new car. This situation called for a new plan with new routing for this complicated wiring system.
The tools for wiring are critical. Using junky terminal crimps and dull cutters don’t make it any easier. The most important tool in a wiring job is the crimpers. Crimp connections often get a bad reputation because of poor installation. A properly made crimp is just as good as a solder joint. The key is correctly sized terminals and quality crimpers. Those cheap combo crimp-n-strip tools are no good; throw them away. They are only good for emergency repairs. You need a set of good crimpers designed for insulated terminals. Klein Tools and KD Tools make excellent crimpers.
The first step is to break down the harness and split up the groups of wires.
Plan the layout of the harness before getting to the car.
It’s very important to properly install wire terminals. A speed stripper really speeds up the process and is a worthwhile investment.
The key to a good crimp is quality crimpers. This pair works great for insulated terminals, the kind used on this car. They also work for non-insulated terminals.
Select the correct size of terminal for the wire and insert it into the corresponding set of jaws in the tool. Using the wrong jaws can result in over-crimping (which breaks the terminal) or under-crimping (which results in a loose connection).
A properly applied crimp should look like this. The insulation is slightly bulged, but not squished. Always tug on the wire and terminal to ensure it is not loose.
Next, locate where the engine side of the harness goes through the firewall. On the Corvette, we used the stock location. Be careful, as sometimes the chosen hole has another function.
The fuse box mounts to the firewall with two bolts. It can be a real pain to install the fuse box; having a helper alleviates a lot of frustration here.
The metal backup plate was trimmed to match up with the firewall.
Inside the car, the bundles of wire were split into groups and routed to their locations. Don’t cut any wire until the entire harness has been routed.
This is the Painless Phantom Key push-to-start system, which includes keyless entry. This system replaces the ignition key with a push button and includes all the relays, which were mounted under the center console in the Corvette.
The neutral safety switch and backup light wires were routed to the shifter and terminated with spade terminals. This makes removing the shifter a no-cut proposition. You may not need to remove it, but if you do, this makes it easier.
All the main ignition wires are 12-gauge wire. These feed the majority of the electrical system. The key to safe wiring is using the proper-gauge wire for the amperage. The longer the wire, the larger the gauge needs to be.
There are two main power feed wires, which are terminated to the large feed wire that connects to the battery. Terminate this with a single large 12-gauge wire terminal. The two wires on one side are smaller than the main feed wire.
Most Painless kits do not come with any ground circuits. Usually this is not an issue, but with Corvettes, locating a good ground can be a bear. Use a ground harness for the rear taillights; use ring terminals and 14-gauge primary wire to provide grounds for each light.
This tech tip is from the full book, LS SWAPS: HOW TO SWAP GM LS ENGINES INTO ALMOST ANYTHING.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://lsenginediy.com/ls-swaps-wiring-harness-and-wiring-guide/
The key to a good ground is a solid connection. The paint should be removed from the metal surface of the ground location. If you can’t remove the paint, a star washer is an alter-native, as it cuts into the metal as the bolt/screw is tightened.
Next, bolt the ground feed to the frame using the fuel pump mounting point as the ground point. By using the same bolt, the number of holes in the chassis is limited and it keeps everything neat and clean.
Then route the ground harness to each light. The taillights ground on the mounting stud. When using speed-nuts, you have to be careful not to over-tighten them or they strip.
Under the hood, separate each wire group just as it was inside the car. There are a lot of small groupings of wire here, so it is important to take each one separately.
As each wire group is positioned on the engine, the harness starts to come together. Keeping each circuit group together can be tricky, so be patient. The hardest part of wiring is the planning.
Selecting the correct wire size for the terminal is critical. Using a terminal that’s too large results in a weak connection. Most terminals are color coded for size. Red is the smallest, fitting 22- to 18-gauge wire; blue is for 16- to 14-gauge wire, and yellow is for 12- to 10-gauge wire. Anything bigger is sold by the size, not color.
Primary wire is typically an 18-gauge wire and is the most common wire found in wiring harnesses. The larger wires that feed heavy-draw circuits are typically 14- to 12-gauge.
The wire in Painless Performance kits runs a little larger than the standard; the primary wires are 16-gauge, with 12-gauge for heavy-draw items such as the headlights.
Opening the box and seeing several thousand feet of wire can be scary. Fear not. It is not that bad; just be patient. The first step is to take it all out of the box and lay it out on the bench or floor. Separate all the bundles. Painless kits come pre-bundled in all the major groups: engine, dash, and tail. From there, they are divided into sub-categories.
Another component used in Gen III/IV wiring is the Weather Pack and Metri-Pack terminal. These are small pins that require special tools to crimp. They are used in every connector on a late-model engine. Most builders don’t have to deal with disassembling and reassembling terminals but if you are retrofitting a stock harness, you do.
The components of MetriPack or Weather Pack terminals are a Molex or nylon housing, a silicone wire seal, and the terminals. The housings are shape-specific; you must make sure that you have the correct male and female components. The terminals can sometimes be specific to the housing as well.
These are the crimpers used for the terminals. They are available in many configurations, and most have ratcheting locks for a completed crimp.
The terminals must be crimped twice, once on the bare wire and once on the silicone insulation. Make sure you slide the wire through the silicone boot before crimping.
Each terminal style has different pin types. All styles lock into the plug housing with spring locks built into the terminal itself. Unlocking these can be a pain; the trick is to use a small pick or unfolded paper clip to unlock it. Every terminal uses a different lock location.
The DLC or OBDII port is a must-have for any LS swap, and it is often overlooked when retrofitting a stock harness. Make sure you grab the wiring harness from the donor car. If you don’t, you have to head back to the salvage yard or take your chances on eBay. (Photo Courtesy Street & Performance)
These are good for the typical project, but there may be a few wires that need to be moved to a different section. Now is the time to reroute any wires. Once inside the car, this becomes much more difficult. Go over each wire and its location and check the car. For example, if you are installing an electric fuel pump under the hood, you need to alter that wire’s routing as it is normally found in the tail section.
All Painless wiring kits provide only the power side of the circuit. Except for a couple of situations, you must provide all ground connections. Although this is typically a simple thing, Corvettes require some additional forethought, as fiberglass does not make a good ground. Pain-less Performance thought ahead on this one, and they offer a ground kit that comes with wire and several terminal strips to provide multiple ground circuits where you need them.
Wiring an entire car requires planning, time, and lots of patience. If you find yourself getting frustrated with a particular section, get up and walk away for a minute. A novice builder should be able to complete a basic wire harness replacement in three to four days. The more circuits and the more complications, such as EFI, audio systems, etc., the longer it takes. But if you take your time and plan out the locations of all the wires before cutting anything, your wiring project will look and function great.
Written by Jefferson Bryant and posted with permission of CarTech Books
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