Pocket

This thread is a general how-to for building a custom LS1 swap harness. For this to work you still need to have your 3rd gen engine harness cut down to essentially IGN and gauges Read about it here: http://www.thirdgen.org/techboard/lt...p-3rd-gen.html (How to prep a 3rd gen harness) Now, lets talk about harness selection You dont have to match your year harness to your year engine. Most of the differences you will be re-doing or replacing. Yes, you can even use the dreaded 98 harness on your 99+ engine/PCM. You also dont have to match the trans type to your engine as the connectors that change between the two are common in junkyards and just as easy to swap out in the harness. All pinouts in this article relate to the 99+ PCMs with a T56 on a 90-92 3rd gen For broken connector replacement try sourcing a S10 vortec 4.3 harness in a local junk yard. All but about 4 connectors interchange freely and the PCM terminals are the same. If you are super cheap and do not want to buy a 4th gen or 4.8/5.3 truck harness this is a viable option as LS1 style harnesses generally go from $150-250. A pieced together S10 harness with outsourced missing conenctors can be assembled for under $50 This thread will NOT be going over LS1 fuseblocks, dashes or anything other than a plain jane LS1 in 3rd gen swap. A thread covering those maybe in the works for later, but not at this time For individual circuits, refer here or LS1tech http://chevythunder.com/ Back to the job, this is a LS1 harness fresh from a 4th gen This is what you're turning it into. Notice the handful of coiled individual wires. These are all the conenctions to the original harness or the power distribution block One final word before we get started. Whenever someone talks about the "3 wire hook up," they are talking about these connectors: C100, C101, C105 An exerpt from this article on the subject http://www.ls1tech.com/forums/conver...swap-faqs.html Quote: when you get a pullout that has the harness on the car, everything is connected except: 3 connectors that were underhood. (named C100,C101,C105) 2 connectors that used to connect under the dash (220,230) so these 5 connectors are the ONLY wires we're worred about. in a nutshell... give ignition power to the pink wires, constant power to the orange ones, take off VATS, and it runs. the other wires you hook up are just gauge wires, reverse lights, ect.... nothing hard. its ALMOST a stand alone harness already... only diff is it will have a couple extra wires left after its hooked up.. not a big deal.. theres one more wire not listed there.. its a thick purple wire that goes to the starter. when it gets +12v, the starter turns the motor over. Now, down to business. Start by labeling every single connector. If you dont know what one's function is, look it up Now remove the covers and de-pin both PCM connectors. Some of the pins you will never reuse, others will be easier to lengthen/shorten with them removed. This also fixes any issues with the 98 harness as the pinouts differ greatly

This ad is not displayed to registered members. Register your free account today and become a member on ThirdGen!

Pocket

Remove the loom and tape. I left the trans wiring loomed as it pretty much isnt changed even with the new layout


Begin to coil up the connectors. Some wires should nearly be free just by removing the loom. Other you will have to unravel completely. No cutting yet


Eventually you will run out of loose connectors and the remaining pile of spaghetti will be continuous. Now is the time to get your snippers. Start by removing the C100, C101, C105 and the under dash connectors. You will not be reusing these in any way unless you are repairing a 4th gen harness so cut these close and throw them away. Once that is done several more connectors will come off but the mess isnt separate yet. Now its time to start cutting commons. Unlike with the 3rd gen commons, most of these are reused as is easier to solder single wires together than 4-5 wires into one connection. There is one main IGN (pink) common that runs pretty much everything thats not injectors or coils related. The injectors and coils have their own common on each bank. DO NOT CUT THE INJECTOR/COIL COMMON OUT, NOR THE LONG PINK WIRE THAT WENT TO THE DASH CONNECTOR. These will have to be immediately resoldered in the exact same place so cutting them would be adding uncessecary complexity to an already overwhelming job. There should be 2 ground commons each with a ring that attaches to the rear of a cyl head. If the car had traction control, the IAT low ref wire (purple) will be attached. Remove the traction side of this. Oddly enough the TPS had all 3 wires spliced and ran to the dash connector in addition to the PCM. You need only the PCM side and the splices can be cut out when the wires are lengthened


When you are done your harness should look like this
Top row:
Dash connector, dash connector, C100, C101, C105, EVAP, Oil pressure sender, AIR, vent solenoid, rear HO2, rear HO2, group of loose wires with the PCM terminals
Middle row:
TPS, IAC, CAM, Crank, MAP, MAF, 3 wire MAF to 5 wire MAF adapter(not stock), IAC, ALT(fbody single wire), CTS(99-02 style), traction control, knock, rev lights(T56), VSS/CAGS/Rev lockout(T56), 4L60E trans
Bottom row:
Front HO2, front HO2, 2 PCM terminals spliced into one orange wire(will save time later), IGN common, GRD common x2
Upper mass is the pass side INJ/coil group with the AC compressor clutch connector still attached
Lower mass is the drivers side INJ/coil group

For this particular swap, the entire top row will not be reused


Now, get a mockup engine

Pocket

Using these pinouts, label each wire for every connector. I like to wrap the wires every 6-8" to cut down on tangles. Label the PCM connector and pin assignment as well as the connector name incase you mix the pin up. There are up to 160 pins and thats alot to get mixed up
The pinouts were recycled from my 0411 swap so ignore the Express van side. Also, Blue is C1 and Red C2. This gets confusing so my pin assignments are labeled by color rather than C1/C2 Ex: R9 = Red pin 9, B42 = Blue pin 42. Some colors changed over the years. For a specific year/model breakdown resort to LS1tech or chevythunder




Drape the wire groups over the engine and plug 'em up. You should get a general feel for the shape of the end harness


Once the routing is decided, bind the groups together with electrical tape. Ensure no connector is pulled taught and has plenty of length

Pocket

Continuing on the pass side


CAM, MAP, Crank, knock added in and the sides bound together with tape


Pulled back off it should be very neat and tight with the huge mess pointing to wherever you are mounting your PCM


Once all of the connectors are fitted and bound to the harness it should look like this. Pull all of the cut commons out of the bundle. The next step is to reconnect them


Break out the soldering iron and connect the IGN commons back in and then the grounds. Be sure to have a runner wire between each of the ground commons connecting them as a failsafe to a bad solder or broken wire. Factory had just about every common fused individually. This isnt necessary, all you need are PCM, INJ1, INJ2 all are ran through the C207 and fused at the stock 3rd gen fuseblock. You can fuse the MAF, HO2s, and trans solenoids if you like but you will have to find places for each. An easy one is the emissions common wire from the 3rd gen harness. Since emissions are gone(for this swap) its an open slot and i like to put the HO2s on there. It would behoove you to double check your work as you go with a multimeter. Setting it to resistance shows two things: continuity and resistance across the joint. Factory wires with crimped on terminals are usually between .6-.9 ohms depending on size and length. Try to keep the new solders under 1.4 ohms since most of the sensors are read off of returned resistance in the PCM

Notice the IGN lead up top. This will be connected to the old heavy pnk from the 3rd gen harnes. You should have 3 ground rings. I like to put one on each cyl head and one to the framerail. You should have one long runner grd left thats not connected to anything, do not cut it off. It will be used on the ALDL
From the big mess, all should have a PCM connector attached except for a few. Starting top middle going counter clockwise: main IGN, grd runner wire, backup lights(manual trans only), INJ1 and INJ2 pnk's

Pocket

he engine does not have to be in the car for the necessary lengths to be measured. This can be approximated by using a common point on the old engine and the new engine. I use the vacuum T on the rear of the LS1 intake as its along the engine centerline and very close to the same on the SBC/V6 distributor. Use a hose/cable to mock the route of the wires to get a length measurement for the PCM location. I used a piece of Romex house wire

This is the stock routing for the harness. Notice how it winds around the HVAC box for no good reason. Routing over top of the blower motor is more direct and IMHO looks better


Finding centerline of the engine and routing the Romex


Along the top of the firewall


Though the upper hole, looped into the factory harness clip and through the fender hole into the chassis


From the interior, I like to run the PCM connectors up to the trans tunnel for that extra few inches to orient the PCM under the dash

Pocket

Back to the harness, bind the measuring cable to the harness at centerline. I set the trans/HO2 connectors to center previously so theres no reason not to do it again


All of the wires will need atleast SOME length added. Here are the longest two and even they need about a foot


Check each wire as you lengthen/shorten it and fix problems as they arise. Going back to redo something is very irritating. It would be a good idea to print off a copy of the PCM pinouts, mark off the wires not used and check each pin as you finish install them
Starting


Finished with all of the engine connectors


Now, the harness still isnt done as several non engine wires must still be added. If you have been keeping a running tally of the remaining pins this should be relatively easy
Add in the org battery wires salvaged from the beginning, IGN lead (dont connect it to any IGN common), tach, P/N lead, relay leads, seral data (ALDL), MIL, speedo output and cruise(if used)

Pocket

Look up your particular C100/C207 pinout for your year 3rd gen. Here is the 90-92
C100 Connections:
Tach to R10
TCC to B33 (4L60E only)
IGN to whatever IGN commons are left on the LS1 harness that are not fused
There should only be one from your IGN common
C207 connections.
B to bank 1 INJ/Coil IGN wire (PNK)
C to R46
D to R50
F to B19
G to bank 2 INJ/Coil IGN wire (PNK)
N to B32 and B34
Depending on the tune the PCM will not allow the engine to start unless either B32 or B34 is grounded. Which is arbitrary but not having it grounded will be difficult to trace. Ground both and dont worry about it anymore


Finish up the remaining wire leads from the PCM
Relays: if using stock 3rd gen units, the dk grn/wht wire is grounded(fans) or given 12v(fuel pump) for the relays to enable
Fans go to either or both B42 and R33. One PCM pin can control both fans, or the PCM can control each fan independently even at different turn on temps if used separately. The tune can set each's turn on temp
Fuel connects to R9

ALDL must be upgraded from the stock OBDI to OBDII. This can be had from any OBDII GM car. The stock OBDI ALDL does not have to be removed, just be aware it will no longer function
Pinout

Serial data goes to B58
Splice the battery power to the PCM battery common and attach the runner ground wire from before

VATS must be disabled both in the PCM tune and in the 3rd gen dash harness wiring. Both are quite simple. Locate the starter kill relay behind the drivers kick panel and connect the two heavy wires at the relay. Depending on year, engine and trans type the colors will vary. One wire will ALWAYS be yellow, and the second either dark green or tan/wht

That should wrap up the harness. Loom it and install. Have fun

1A Dan

I don't know what a lot of us would do without ya on this electrical stuff. Subscribing for when my harness arrives.

__________________

1987 Trans Am, work in progress
2008 Pontiac G8
Retired: 1984 Camaro "ZF" 2.8L, 1989 Camaro RS
Customer Service Manager, 1A Auto Parts

cam-

This is going right into the sticky nice work Pocket

__________________

Jaysz28

Awesome write up man!

Great job

thanks!!!

-jason

V8Rumble

OUT-Freakin'-STANDING! Thanks Pocket!!

BlueZee28

Jon (Pocket) is THE MAN.

Yes, I'm the lucky duck that got a flippin' sweet harness out of this tech article. Thanks again Jon. Oh, and for anyone that may do business with Jon in the future, he is an excellent person to do business with, I highly recommend him.

__________________
<>< Nick <><

LSX swap in progress...

For More Pics Click:
http://www.omnipotent-goku.com/iroc/gallery/album140

1A Dan

That's the exact smiley I was trying to find for my comment. glad someone posted it

Shift06

I am already next in line lol.

screeminchicken

This should be stickied up top. I like how he even went into details on how to extend the wires. Tips like to remove the pcm connectors for easy sorting etc.

1st class.

where is five7kid to sticky this thread.

five7kid

It's linked in the LS1 swap sticky.