As with other LS components, a massive number of computercontrol, harness, and electronic equipment options exist for this popular engine platform. Most swappers adapt the factory electronics to the particular F-Body, but installing aftermarket controllers are certainly an option. If you don’t want to adapt the EFI and drive-by-wire gas pedal technology to your F-Body, then installing a conventional distributor and carburetor on your LS engine is an option. Many wiring harnesses and installation kits are available for LS engines. For my particular project, I adapted the modern LS EFI system.
This Tech Tip is From the Full Book, SWAP LS ENGINES INTO CAMAROS & FIREBIRDS: 1967-1981. For a comprehensive guide on this entire subject you can visit this link:
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For a first-time engine swapper, buying and installing a complete wiring harness and adapter kit is the best option because creating or modifying a wiring harness and adapting the drive-by-wiring controls is incredibly complex. After all, you want to get the car on the road as soon as possible. Typical kits do not require an incredible amount of electrical acumen; in fact, many can be installed by connecting only four wires.
Although wiring may not be your favorite work, it’s often necessary to complete a project. One option is to pay a professional to do it, and certainly there is no shame in that. The LS engine is pretty straightforward when you can get it with a programmed ECU and matching wiring harness. Beyond that, there are a few common issues when performing this swap.
The LS engine is a bit of an oddball when it comes to gauges and locations to put them. But the LS wire bundle is a masterful stroke of genius because you don’t have to wire anything you don’t want to! Since the ECU uses all of the vital parameters that you’d have on the dash to keep the engine running smoothly, you can tap into those systems quite easily using the wiring bundle from the LS harness. Most of these parameters, including RPM, water temperature, oil pressure, voltage, and more, are already coming out of the wiring harness. You need to wire it to the correct corresponding gauge in your gauge cluster. There can be a few exceptions and I cover the ones that you are most likely to need and run into.
Tach wiring is fairly straightforward; it is spliced in from the wiring harness and ECU, typically PIN 10 and a white wire (1999 to 2002 have a red connector, 2003 and later have a green connector). In most cases, all that is required beyond the wire hookups is that the tach itself should be set to 4-cylinder or 6-cylinder mode depending on the make and model of your gauge. Sometimes you need to tap the coil wires themselves (usually pink) to run to your tach.
This takes care of most LS tach wiring; however, a few people require a small additional resistor known as a “pull-up” resistor. A wide variance is possible for those who may need to modify the tach signal. You know pretty quickly if you need to do this when you start up the engine and the tach acts erratically or reads inaccurately. Today’s aftermarket tachs require a ground wire as well as a 12-volt source and exciter wire. The exciter wire is the one that can necessitate the “pull-up” resistor.
You need a 5,000-ohm 1/4-watt resistor or a 4,800-ohm 1/4-watt resistor. Often a 680-ohm 1/4-watt resistor works; a best practice is to start with the 5,000-ohm 1/4 version and work your way down. Besides, resistors are cheap and plentiful. You need to run this wire from a fuse-protected keyed (only operates when the key is turned to “on”) 12-volt source and then spliced into the wire from the harness to the tach. Start it up and see if it’s working.
The LS engine has a variety of ways to measure water temperature. Most notably are the two ports on each cylinder head. On both heads they are at the same location, farthest to the driver’s side of the head. You’ll find a plug that needs an M12 x 1.5 adapter to run an electric gauge. Because the size of the hole, a mechanical gauge doesn’t fit.
Auto Meter has made an adapter for the electric sending unit (PN 2277). This adapter fits right in and has a 1/8-inch NPT port that accepts most sending units. Auto Meter warned me that a smaller sending unit (PN 225) might be needed.
For my Stack cluster, I wasn’t able to use the larger fitting because the bore was too tight for the sending unit. I thought I could be clever and bore out the fitting, but that ended in failure. I turned to the heater hoses instead. I used an Auto Meter (PN 2280) to help. It’s a 5/8-inch hose adapter that accepts the 1/8-inch port size. I used 5/8 inch because it is the “feed” side of the heater box, meaning that hot engine coolant enters the heater core through this hose and exits out the 3/4-inch hose.
The LS engine has an oil pressure plug similar to the small-block in the respect that they are in the same vicinity. That’s about where the similarities stop. This plug requires a special adapter to run 1/8-inch NPT sending units. Auto Meter sells a brass fitting (PN 2268) that allows you to use this pressure port for the cockpit gauge. Auto Meter reports that you can run a short piece of pipe or braided hose from the oil pressure side and it does not diminish any readings you get from the gauge!
Here’s where a few things get tricky. The engine harness needs a port to tell the ECU how much oil pressure is being generated. That typically is the back slot behind the intake in the traditional location. If you use this for your gauge, you have to figure out something else to make the ECU happy,
The solution is a modification to the oil cover plate located right above the oil filter. The oil pan from Mast doesn’t have this option, but I show you how to solve that problem. Drilling and tapping this plate gives you an excellent way to add a gauge without making any unsightly changes. You need to keep everything away from the heat since the headers are directly in front of this piece.
Oil-Pressure Sending Unit Installation
You need to cut off the excess material to make room for the NPT tap, which is tapered. Don’t cut off so much that you have nothing left to thread to. However, you need to remove roughly 1/2 inch to fit the sending unit. (Photo Courtesy Auto Meter)
Use a 5/16-inch drill bit to enlarge the center. (Photo Courtesy Auto Meter)
Chase the drilledout section with a 1/8-inch NPT tap. You need to go slow and steady to properly clean metal shards out of the oil fi lter port. You obviously don’t want metal debris fl owing through your engine. (Photo Courtesy Auto Meter)
You can now screw the oilpressure sending unit into place; snuggly so as not to leak but not too tight to cause a crack.
For my oil pan, I had to be a bit creative. I quickly noticed that the oil pan doesn’t have the typical plate that can be modified. It only has two -10AN ports that are meant for an oil cooler (I mentioned that Mast doesn’t mess around when they build engines, right?). I called Mast and they informed me that the rearward-most port is the “feed” line and provides accurate oil pressure readings. Just as with the stock oil plate, I was able to drill and tap the aluminum -10AN fitting to accept the 1/8-inch NPT sending unit. I added a 90-degree elbow to clear the side of the block to allow the sending unit to clear and not interfere with the hot header. I plan to take the advice from Mast and add an oil cooler.
The good news about the oil temperature gauge is that it doesn’t need any pressure; it only needs to be submerged in hot oil to work properly. There are several ways to get the proper oil temperature. You can branch off the oil-pressure sending unit with a T-fitting or you can make its own special slot. Chances are, your wiring harness isn’t using the low-oil-level sending unit. On the passenger’s side of every LS pan is a plug that the stock harness uses for an oil level warning light.
I was able to find the right fitting for my 1/8-inch NPT sending unit. I used a specialty pre-tapped aluminum fitting from Speedway Motors (PN 481201). It allows me to use the sending unit and not make any major modifications. Typical operating temperatures for the LS engine are roughly 195 to 210 degrees F. If you plan to track your car and start seeing temperatures above 275 consistently, you need to add an oil cooler.
You must maintain the correct fuel pressure of 58 psi at all times in an LS engine to realize maximum performance. I used an -8AN adapter from Earl’s that allows me to run a 1/8-inch NPT solid-state sending unit that matches the stack EFI injection stack unit (PN AT100196ERL).
To check the fuel pressure, insert the key into the ignition and turn it to “on” so the EFI system primes itself. It should turn the fuel pump on for 2 to 5 seconds and shut off if the car is not running. This allows you to check the gauge and fuel system leaks.
A number of automotive businesses, including Painless Wiring and American Autowire are more than happy to build a wiring harness for you. It will be more costly, but it’s an option if you don’t have a lot of time. You can, of course, build your own wiring harness as I have shown you.
Both companies make great kits to suit any need and in many cases make kits that far supersede anything that came from the factory on the first- or second-generation F-Bodies. I chose the American Autowire kit because I’ve had experience working with their systems and felt comfortable using them again. The best advice I can give you is to go slowly! Take your time and work with the components one at a time. It can be a bit daunting when you see all the wires in one giant bundle, but if you look at each circuit individually the bigger picture tends to take shape.
You need to know a few things up front before you order a harness: the transmission needs, whether you are sending a harness to be reworked or purchasing one, the length of extra harness (crucial if you want extra to mount the PCM under the dash), the oxygen sensor requirements, and the fuse/relay box needs.
You can use a wiring harness from a junkyard or you can have one made out of whole cloth but you should be prepared for some extra cost.
Fabricators usually ask questions about your particular build. You need to determine which computer you are going to use and specify which transmission will be installed. If it’s an automatic, you need to program the ECM’s shift points and transmission functions or you’ll have to use an external stock ECM or aftermarket version. You also need to determine if you are going to be running A/C. In addition, you need to decide whether to use a speed-density system or a mass air system.
The final consideration is the length of your harness. To figure that out, you need to decide on the mounting location of the computer because that dictates the length of the harness. You can mount the ECM in the passenger’s compartment and run the wires through the firewall. If you choose this placement, you need a longer harness than if you mount the ECM in the engine compartment.
Wiring Harness Installation
The Mast wiring harness comes prelabeled with many of the popular connectors already marked. It’s nice when things are so easy. Since the Mast harness is customized and pre-routed for the particular engine, connecting the wires is a no-brainer. Decisions about the fuse box and ECM are crucial. Those need to be free from heat, free from vibrations, and in an easy-to-access area.
Here’s the Mast wiring harness that came with the engine. Everything is well laid out and fits to the block (doing its best to remain hidden).Step 3:
The M-90 DBW ECU from Mast is a pretty solid piece. It comes with rubber grommets. It’s up to you to fi nd a good place for it away from vibrations, heat, and excess moisture.
This is the original gas pedal; it has to go. The drive-by-wire pedal will be mounted to the fi rewall.
This jumble of wires is not as confusing as it looks. Everything has a place and there is a place for everything. Go slowly and it will make sense very quickly. Because each wire has only one way to be routed and only one specifi c counterpart to be plugged into, routing/connecting the wires is a simple procedure. After it’s clicked into place, tuck the wire behind anything close, such as the injector.
The American Autowire (AAW) kit replaces the old front body harness further along in the build.
Removing the old wiring harness can be difficult but if done carefully I can probably resell it at the swap meet and maybe recoup some of the cost. Many of the wires from the factory are held in with bent tabs or clamps. It pays to follow each wire cluster until you get to a junction then gently remove it.
Here are the original gas pedal (left) and the new DBW gas pedal (right) side by side.
Once all the wiring has been removed, you can start to plan your wiring setup more carefully.
Here’s everything you get in the AAW wiring kit: a new ignition switch, brightbeam switch, and headlight switch.
The idle air temperature sensor is an easily missed connection. This one just plugs 10 directly into the K&N air filter.
The Mast harness comes with three connectors under the dash in addition to the main wire bundle. They are: OBD-II port (upper right), drive-by-wire port (right), and ECU interface (left). Determine the location in the foot well to mount it, drill two pilot holes, and then screw the plug down with sheet-metal screws. Your wiring harness most likely only has the OBD-II port and drive-by-wire plug.
To get all these wires in the dash, I had to cut a 3-inch access hole in the firewall. I use a 3-inch rubber grommet to make sure air and gases don’t enter the cab. Placement of the hole depends largely on what you want to do. If you want a hole closest to the gauges for ease of wiring such as I did, this is a good location. Others have put a hole behind the engine to hide the harness. The choice is up to you.
This is the bundle that comes out of the Mast wiring harness. Most of these wires aren’t necessary for the entire wiring. Some go to gauges while others are crucial, such as ignition and key-on cycling. Wires that are not used are capped. It helps to have the wiring diagram handy to make sense of it all because each wiring harness is slightly different. This harness came with a set of instructions. I pulled back a good part of the sheathing to reveal the wire markings to determine which was which.
A ground strap can be found at any local auto parts stores, and you need to be sure your electrical system is properly grounded. Because this frame was powder coated I had to scrape some off to make sure the ground strap had excellent metal-to-metal contact.
Wiring Harness Hookup
Don’t let this giant bundle of wires intimidate you. I like to call this type of automotive work a “process of elimination.” Once the engine arrived at my place, I promptly removed the wiring harness and started working on the engine accessories and other pieces. After a while, the harness had to go back on and I couldn’t remember the right way to install it. Thankfully, the weather pack plugs and configuration allowed me to figure it out quickly. It’s pretty hard to mess this up when everything has a specific place and corresponding connector. If you organize them, everything should go smoothly.
Length of Harness
Any wiring harness company worth anything asks you how much “extra” length you want in your harness. The extra length allows you to mount the ECM and the fuse block in a suitable location. The location determines how much extra length you need. I’ve seen extra lengths range from ultra-short (where the components are mounted in the engine bay), to super-long, as in 3 feet or longer (to accommodate mounting inside the passenger compartment). This extra bit determines where you can put your ECM in the vehicle. It might be worth figuring out where you want to put your computer well before you order a harness.
OBD-II Port Location
Any wiring harness should come with an OBD-II port. This is a standard port for all newer vehicles. It allows you to plug in a scan tool or laptop to “talk” with the PCM to program it further or troubleshoot codes that are being thrown.
The wiring harness side is a female 16-pin J1962-type connector with two rows of 8 pins. The government standards mandate that this must be within 2 feet of the driver’s position. This is the best position because it allows you to use the scan tool or laptop while in the driver’s seat to turn the car on or off with the key.
I located it under the dash within easy reach and away from the pedals. Of course you can position it anywhere you like. People who want the clean look put it in the glove box.
Drive-by-Wire Pedal Installation
Because I have a drive-by-wire setup I need to fabricate the housing for the electric pedal. I built a simple box out of 1/8-inch plate and will weld it onto the floorboard of the car.
I found a good spot for the pedal, not too close to the transmission hump and not too close to the brake pedal. I also made the gas pedal a few inches closer to the fl oorboard than the brake pedal to allow for better heel-toe braking and 2 revving.
First, I matched the mating plate to the pedal. Then I drilled a couple of holes so I could mount it to the bracket. I welded a couple of anchoring nuts on the backside because I want to be able to remove the gas pedal if something happens.
After finding a decent place to mount it, I tack welded it in place, making sure it goes to full throttle without hitting the floor. I also looked carefully at the brake pedal height to see where it is in relation to the gas pedal. I plan to drive the car aggressively and will be doing a lot of heel-toe braking and gassing. A simple MIG welder is suffi cient if you make sure the welder is on a low-amp setting and you’re using the correct rod for the job. You don’t want to burn through the thin sheet-metal floorpan.
I removed the pedal to finish welding the box. I added a couple of support areas due to some fl ex in the box as I articulated the pedal. A full box weld isn’t necessary. Make sure nothing on the other side is near it; it could start a fire to burn something important;
To hide the main harness wire, I cut a hole in the firewall, added a grommet, and fed it through. A lot of people like to put the hole directly behind the engine to clean it up even more. You need to avoid routing the wiring harness too close to the exhaust or other hot engine parts. Routing the harness behind the engine is fine because there is not excessive heat in this area.
After I put the pedal back on the bracket, I connected it to the wiring harness.
Oxygen Sensor Requirements
Many states (including California) have pretty strict emissions standards so it might be worth keeping the front and rear oxygen sensors. Some states have looser emissions standards, so you don’t need them. Either way, make sure to communicate this to the harness builder. Also, keep in mind that you need to communicate your oxygen needs to the person who is going to reprogram your PCM.
If you live in a state with tough emissions standards, it might be worth looking into the E-Rod line of products from General Motors. These are emissions-legal exhaust systems that meet many state requirements.
Fuse Box and Relays
If you have a stock harness, chances are that you won’t have a relay and fuse block to work with and you’ll have to be creative. If you chose a premade wiring harness, a fuse block can be integrated into it.
You need a 12-volt power source leading to the relay, a trigger for it, a ground wire, and the power wire to whatever it is you need to power. In some cases, you can pay a little extra for the ease of an incorporated fuse/ relay box.
I found this extra feature in the Mast harness to be a wonderful lifesaver. Not only did it come with fuses for things such as the fan control, but it came with a fuel pump relay that allows me to run a wire directly to the fuel pump and keep things ultra-tidy.
Because various transmissions require different setups, you must determine which transmission to install. If you are using an older automatic or manual transmission, and want the ECU integrated into the harness, you need to specify the transmission and that you want this extra feature.
Adapting an LSX Wiring Harness
Many LS owners are on a limited budget and don’t have the funds to construct a custom harness for a major rewiring job. You may think that wiring is too challenging and difficult to tackle yourself. If you go slowly and carefully you can adapt a truck wiring harness to your particular application. You simply break each sensor down into its individual components and wires.
For most enthusiasts, the mechanical part of building a car is second nature while electrical wiring is more of a challenge. I was a complete novice when it comes to anything wiring so I went to my local LS guru and custom fabricator of all things GM LS, Nate Shaw of One Guys Garage. Nate has made many custom-length wiring harnesses. He strives for a virtually invisible wiring harness that is completely functional but leaves car show visitors wondering where it is when looking under the hood.
I bought an inexpensive wiring harness from a GM truck equipped with an LS engine. I combined it with a few off-the-shelf parts to build a custom wiring harness for less than $100. Be prepared to spend anywhere from 8 to 12 hours on the build. However, this is a great way to get into the LS engine family for the person who has a lot of time but not a lot of wallet.
You need to work slowly and methodically because this is intricate and detail-oriented work. The list of pin outs for the typical 1998–2002 Corvette wiring harness is long but they haven’t changed much over the years. If you completely strip the PCM connectors and only plug in the parts you need, this part of the project will be completed in no time.
Wiring Harness Installation
I started with the wiring harness out of a 2000 Chevrolet Suburban truck that cost $25 from a local junkyard. It was such a bargain that I bought two! It originally came wired for an automatic. More specifi cally, this was designed to fi t with a 4L60E transmission, but I am going to upgrade it to use the 4L80E for its robust strength, as I am looking for something that can handle more than 600 hp. For a build like this, you may use whatever port you wish to 1 match the transmission you’re going to use.
If your wiring harness came from a manual transmission car, you don’t have this plug; that’s something important to look for when planning your wiring project.
I cleared out all the wiring coverings and plastic retainers. This helps get a visual of the harness and get it down to the basics so I can route every wire exactly where I want it to go.
Take apart the PCM connectors to get at the wires; they slide right off without much effort. The back cover just clips into the metal holder. Make sure to take care and not snap off the clips so it can go back together smoothly. The front cover (blue or red) slides off easily with a small pick.
An easy trick to removing the wires is to use your fingernail and pry up slightly on the tab. Label your PCM connectors so you don’t get lost.
Pull out your wiring diagram and follow along. Going on from this point takes a fair amount of concentration and attention to detail. Each plug designates one of the sensors corresponding to the ECM. If one of the plugs is not in the right location, the ECM does not know what to look for and what is wrong. If done correctly, you will have taken the mystery out of wiring.
Laying out the harness allows you to see where wires, connectors, and terminals need to go. It also keeps everything organized.
You need to cut or remove all the wire terminals and label the PCM connectors to help you later. Typically, when you find a pink wire in the harness, it’s used when the key is on or “key-on” type wiring; when you see an orange wire that is usually for 12-volt full-time power.
Pay attention to how each of the PCM connectors are numbered. On each side, the red and blue look similar but are numbered with each pin to do a very specific job. Be sure all the connections have been made and are correct. Follow the diagrams and wiring locations that were provided, General Motors used a lot of them and they are fairly universal.
Separate things into two piles. One is a wire bundle of things you need later and the other is the throwaway pile. You often need to wire in the post-converter oxygen sensors, EGR connectors, and mass airflow sensor, particularly if you are converting to a speed density setup. In addition you often need to connect for the A/C compressor, clutch, and transmission wires if you are going to convert to a manual transmission.
The fuel injector connectors need to be replaced because I plan to use standard LS1 injectors (right connector). If you are using truck injectors (left connector) you can skip this step.
To complete the job, you need the following:
A. Correct connectors for the EV1 fuel injector.
B. Relay to power the harness, sensors, and injectors.
C. Hoop connectors for the ground wires in the system (top bag), an 18- and a 20- to 22-gauge wire terminals to rewire the PCM connectors (middle and bottom bag).
D. OBD-II connector (usually from the junkyard); replacing it is necessary and straightforward.
E. Fuse block to protect the circuits in the wiring harness. The factory harness typically incorporates this in the main fuse block. Since I can’t take the entire fuse block out of the truck I have to bypass it; this is a crucial component to the life of your wiring. F. Extra wire (top) to extend a couple of pieces and female blade-style connectors (bottom) for other connections.
The closest wires are the ones I plan to throw away and the tightly bundled wires in the back are the wires and pigtails I am going to reuse.
I had to purchase an injector driver box to help run low-impedance injectors. Here, I am installing large high-capacity injectors so it was cheaper in the long run even with purchasing the injector box. This step isn’t necessary if you are going to run high-impedance injectors. I just wanted to include it as a lessexpensive alternative to fancy injectors.
Next, I need to run the wires to each of the respective items. Then I’ll run each wire back to the simulated PCM position. You can be judicious with your placement because you are in control of the length of the wire.
I trial-fitted the PCM connectors behind the engine. I measured the placement in the car and determined the location. This step is critical in getting a harness that fits well. Depending on where you decide to mount the ECM you may have varying lengths of extra wire. I measured the distance from the engine to the location of the ECM on the donor car.
Here’s a good look at removing terminals from a weather-pack connector. You need a very small implement to stick inside to remove the wire. This is a truck alternator plug-in; I removed one of the wires because the LS1 alternator only requires one exciter wire. I used a small-bladed screwdriver to gently remove the extra wire. A small tab on the inside of the connector releases the wire.
After studying the wiring diagram I found the correct hole for the alternator wire. It was located on the red (C2) PCM connector in slot 15.
This Matco wire crimper (PN TCT1028) is a useful tool. It has all the correct crimps and allows you to breeze through the tedious work of crimping all new connections.
After a few sensors, your wiring harness should look similar to this. Go slowly and do one sensor at a time; this reduces errors and ensures a perfect fit. Connect the wiring one at a time. This reduces any issues around the ECM block and also reduces chances of tangling or mismatching any sensors. Make sure to follow the diagram for best results.
I’m attaching the coil power wire to the fuse block, and the other end is attached to power from the battery through the relay. One fuse provides full-time power for the PCM, but the rest requires the ignition switch to be turned on. The other fuses are used to power the transmission connector, oxygen sensors, and injectors. The wire must first be stripped and the appropriate 21 end put on for each type of connector.
All of the pink wires from each injector run to the fuse block, and are spliced together. The other wire at each injector triggers the injector to supply fuel to the head. The pink wire provides the power.
All the information comes off the PCM connector. Combine that wire with the 12-volt power wire and two-ground wires and the installation is complete. To wire the OBD-II sensor, you need the green wire from the PCM in the upper-left position. Two ground wires are found in the two middle positions (shown). Finally, you need a constant power source that comes from the orange wire (lower right). You can tap into a constant power source from the battery or even the back of the alternator.
After you’ve collected all of your power wires from your injectors, you should have something that looks similar to this. Remember, orange is constant power and pink is “key-on” power.
I have run each wire to each connector and kept the wires as inconspicuous as possible. I recommend putting them close to the intake and routing them tightly. The process was repeated for each sensor on the engine and for the transmission. You can use any type of sheathing you wish. You may even use the original GM sheathing. A number of sheathing products are on the market. I used Bentley Harris Roundit 2000 braided sleeving from Cableorganizer.com. This stuff is a bit pricey and puts me over the $100 mark for this project, but it looks totally killer. Remember, it’s the little details that really make a car stand out.
One of things you need to do before you can fire up your engine is to get it programmed to fit with your new setup. Make sure to discuss all your options with the programmer. (Even if you choose to buy a complete harness and ECM from a junkyard, you still must reprogram the computer.) Most GM donor cars and trucks you’re most likely to run into have the VATS system. You will have to calibrate that factor out of the tune. Also, since most of these swaps aren’t subject to emissions standards (see your local state laws for compliance) you may want to eliminate the two rearward oxygen sensors because you won’t be running catalytic converters.
Here’s a short list of things that need to be changed when you send your ECM to be programmed or when you purchase one:
- Fuel type
- VATS disabling
- Transmission (shift points, stall converter, manual versus auto, converter lock up, etc.)
- Changes to the engine (for example, cam swaps, displacement changes, forced induction, etc.)
- Power versus economy tunes
- Speed limiters
- Pedal engagement, if you’re using a drive-by-wire system
One nice feature of buying a completed and dyno’d engine (like mine from Mast) is that you get a fully programmed engine right from the builder, with no guesswork. Mast provides the tuning software free of charge on their website; a proprietary data cable that costs extra if you want to fiddle with the tune.
Written by Eric McClellan and Posted with Permission of CarTechBooks