Updated: Sep 21, 2021
I already know why your here. Against everyone's best judgement, even possibly your own best judgement you went ahead and ordered that too good to be true LS standalone harness on eBay, amazon or Aliexpress for ~ $250.
You watched and waited all day for the post man to deliver it, you open it up only to find a harness in cheap plastic conduit with a wad of unlabeled wires, un-assembled relays and not a single instruction sheet in sight. Your wondering now if you should have just spent the extra money to get a name brand harness.
Well, don't sweat it that's what this guide is for.
I went through the same ordeal when I purchased this harness off of eBay earlier this year for "research purposes". I figured it would be easier than making my own and cheaper than buying a PSI or LSX specialties harness for my 1981 C20 LS swap.
Thankfully for you, I have some prior experience with standalone harnesses and I was able to get a PDF from the manufacturer of the harness wiring which I'll be sharing with you.
What is a standalone harness?
The basic purpose of a LS standalone harness is to take what would normally be an assortment of grounds, Ignition (IGN) 12v, and constant 12v wires on a factory engine harness, and tie them into a handful of easy to wire sources to supply essential engine functions like Ignition, Injectors, etc.
Fortunately for us on stock harnesses; basically all solid pink wires are IGN 12v, solid orange wires are constants and solid blacks are grounds. You can tie each group together to supply power for the harness.
The advantage of buying a new standalone harness is most of the time they are built using new wire and components, meaning they are more efficiently wired for better routing in the engine bay for swaps where you may need to place the ECU in a more convenient location.
The particular harness I bought has just a few main wires that need to be connected in order for it to serve its main function; starting and running a swapped LS engine.
How to install the harness on the engine:
This is one of the easier parts of the process,
You will notice the Harness is basically split into 2 sides:
The driver side; containing the
Driver side (Bank 1) Injector connectors
O2 Sensor connector (bank 1 Sensor 1 (B1S1))
Coolant temp sensor (ECT) connector
Throttle body connectors
MAF (Mass Airflow Sensor connector)
IAT (Intake Air Temp) connector. *Note that on later year engine the MAF sensor may include the IAT sensor resulting in one connector instead of two.
The passenger side; containing the
Passenger side (Bank 2) Injector connectors
A bit below you will have your
Crank shaft position sensor (CKP) connector (Right behind the starter)
O2 Sensor connector (B2S2)
Branching off the back should be your automatic transmission connectors if you opted for the auto trans wiring
Main transmission connector
Transmission speed sensor (TSS)
Right between the two sides should be your:
Camshaft position sensor (CMP)
Knock sensor connector.
Lay the harness on each appropriate side of the engine and connect each connector to its respective place, ensuring each plug goes in with a solid click, you should not be able to pull out any plug by pulling on them without lifting up the locking tab. I will go over the grounds and starter wires later on, for now just ensure every plug has a place and is secured well.
Now would be a good time to go over the injector connectors, hopefully you did your research and chose the right injector style connectors when you ordered your harness, if not don't sweat it, I was sent the wrong connector style but that can be easily fixed by some pigtail adapters.
This is the part where you need to pay attention, especially if you haven't ordered your harness yet.
There are three main types of injector connectors you will come across:
Mini Delphi / MULTEC:
These will be on almost every Vortec engine (4.8, 5.3, 6.0)
If you order a harness make sure its specific to Vortec engines using the Mini Delphi injectors, however i found most chinese / ebay harnesses all are LS1 style using ev1 connectors so adapters are most likely neccesary. This particular harness comes with the proper pigtails to install on a vortec engine.
EV1 injectors can primarily be found on the early LS Car engines LS1, and LS6 to be specific.
This is what Most of the eBay harnesses I've seen use as injector connectors.
If you end up buying a LS1 Style harness here is the pigtail adapter you will need:
EV6 injectors can be found on everything else basically, later model engines like the LS2, LS7, LS9, LS4 LSA, and almost all the Gen IV truck engines.
This is a common injector style and can be found on pretty much anything after 2007
Lets get into the details:
On my harness, and hopefully yours there is two main grounds:
The first is on the ECU (Engine Control Unit) end of the harness, it should be solid black with a ring terminal on it. attach this securely to a clean metal surface (Ideally the same place your battery grounds to.
A good way to test if your area has a good ground is to grab either a 12v test light or a multimeter:
For test light users attach your clip to the battery positive, ensuring your battery is properly connected to the vehicle,
Touching the location you wish to be your ground should result in a bright constant glow of the bulb, this means your location is completing a proper circuit.
For multimeter users, switch your meter to measure DC Voltage ( _-_20 on most meters), hold your positive probe on the positive terminal on the battery, touching your desired ground location with the black probe should result of a constant reading of 12V (May be more or less depending on your batteries level). Another way is to switch the meter to continuity (Beep mode), touching the red probe to your battery ground and the black probe to your desired ground location should result in a constant beep.
The second ground should be somewhere in the back of the engine inline with the injector/ Ignition portion of the harness.
This should be attached securely to the back of the heads, the back of the block above the bellhousing bolts, or the bellhousing bolts themselves. Just ensure your surface is clean and bare.
There are only 2 sets of wires you need to worry about in regards to your positive battery connections.
There are two ring terminal red wires located on the passenger side portion of the harness,
These will be connected to the main battery starter lug, the same one your positive battery cable is connected to. This will be your battery constant.
The other should be coming off of The ECU relay, look for the relay with long red wire coming off of it. This is your IGN wire, this wire needs to be sourced from a wire that turns on with the key, but stays on while cranking. If you are swapping into a older vehicle, the wire that supplied the distributor 12v, will be perfect.
Once these are connected you should hear an audible click coming from the ECU relay when you turn the key on.
You'll notice there is one other relay with a few less wires coming out of it this will be your fuel pump relay, lets go over this one now.
Fuel Pump Relay:
This is probably one of the most confusing parts of the harness if you've never messed with 12v wiring and don't understand what a relay does.
First ill explain how to wire the relay then ill explain why.
You should have received some relay terminals with the harness, don't lose these, you'll need them now, but incase you didn't receive them or need a few hundred extra here you go.
You should recognize that the fuel pump relay only has a Green wire (could be different for yours) and and ground. The green wire is our Signal wire coming from the ECU. What we need to complete the circuit is a battery constant and a send wire for our fuel pump.
Now I believe that the harness manufacturer could have saved us some headache by pre installing the battery constant for us, so since they didn't lets fix that first.
Conveniently both relays will end up sitting right next to each other in the mounting location of your choosing, so lets tee off of the ECU Relay's constant power.
This will be the Thicker red wire going to pin 30 on the ECU relay, I'll let you decide the best option for splicing a new wire in, but i chose to just cut the wire about 3 inches down from the relay, strip the wire, then add a wire about 4 or 5 inches long of the same gauge wire that will reach the fuel pump relay. once teed, just strip the end of the new wire and crimp the relay terminal onto it, the terminal will then slide and click into pin 30 on the fuel pump relay.
Then the last step is our Fuel pump send, Simply get a length of wire (16ga or thicker) that will reach from your relay location all the way to your fuel pump wires, on the fuel pump end connect this wire to your fuel pump positive wire, on the relay end crimp the terminal on and insert it into pin 87.
Once complete your relay should look like this
Now a quick explanation of what we just did:
The relay acts as automatic switcher in a sense, when it receives signal on pin 86, it sends 12 volts to pin 87 as long as it has ground (Pin 85) and 12v constant (Pin 30)
The green wire coming from pin 86 goes to the ECU, when the ecu demands it, it sends signal through this wire which will then activate the relay, turning on the fuel pump.
Wrapping it all up:
If you've gotten this far, it means your basically done with the fundamentals of the harness. You should now be able to start the engine if your ECU has been properly configured.
There are still a few wires left in that bundle there, as promised here is the wiring diagrams from the manufacturer, I've added them to a separate page so you can access them easily:
These wires do not require being hooked up to run the harness, instead these are wires for your gauges, check engine light, and a few other odds and ends.
And that about sums it up, if you have any questions feel free to contact me on my socials, and be sure to follow me on them for more updates.