LTX and LSXPutting LT1's, LS1's, and their variants into Third Gens is becoming more popular. This board is for those who are doing and have done the swaps so they can discuss all of their technical aspects, including repairs, swap info, and performance upgrades.
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This thread is a basic guide to stripping a 3rd gen harness and preparing it to be mated with a new PCM whether its a LT1, LS1, 0411 SBC, aftermarket or generic carb
Retaining part of the original harness allows you to keep the stock gauges without rewiring the interior harness. It also makes finding IGN power easy for the new harness
Ok before we begin, Ill get on my soapbox and try to save a bit of money. If you have a 90-92 TPI do not cut the first wire on the harness. Sell it
Buy a V6 or TBI harness and modify that one as they are significantly cheaper and the sale of the SD TPI harness should net you a good chunk back
Everything V6/TBI/TPI about your old harness is being removed
Next lets talk about harness selection. Match the trans type of the harness to the original trans equipped in the car. This will save you tons of headaches with reverse lights, pedal wiring and what-not. Dash harnesses are trans specific and are VERY rarely swapped.
Ok lets get started. This is most of a V6 harness pulled from a 91 camaro. Notice the coil, dist and AC wiring is hacked and in some places missing. Do not fret as none of this is retained
Label all of the connectors you know, namely the ones that are connected to your gauges
Next strip all of the loom/tape from the harness so you're left with a giant pile of spaghetti
Now start bunching up individual connectors and taping them back so they dont get tangled up so much
All of them dont have to be done, just the more you do the easier the harness will be to separate
Max pics reached
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Now the cutting starts. Located the fender grommet and cut all of the wires on the front/rear of it. Do not throw this piece away. You can hollow it out and run the new PCM harness thru the existing hole with this connector or put the cut bunch back in place to seal the hole if the PCM is elsewhere
Next cut the C207 connector away from the ECM connectors and put it in the keeper's pile
Now rummage thru the spaghetti and cut out any common you find. A common is where multiple wires are spliced from the factory. The usual suspects are grounds, IGN, emissions, AC etc
Continue separating the now loose connectors while bunching the still connected ones together
When you are done it should look like this
Starting where the loom ends on the C100
Fan relay and all related wiring. One brown wire should go to the C100 strait to the fan fuse
Brake warning light
Fuel pump relay and related wiring with separate fuse/holder
Coolant gauge
Oil pressure sending unit
Power dist off the starter (can be moved anywhere)
Starter soleniod wire
Emissions common
IGN with tach
Power dist with ALT connector
2x GRD
TCC with plug
Bottom left is the HVAC power connector
Bot middle C207
Bot right fender grommet
Top middle ECM connectors
Top right pile of unneeded engine control connectors. All the V6/TBI/TPI stuff is in here
The job is essentially done. The relays can me moved by lengthening a few wires to anywhere in the engine bay. I do not like the firewall mount so I moved it under the fender for my first swap. My second i found a cute little relay/fuse center from a 98 Cadillac STS
Since it contained enough relays for my swap and ample fuses, I cut out the large 3rd gen relays and wired them into this and mounted it near my battery
Some wires can be removed depending on your selected options
The ALT pigtail can be cutout if using LS1/truck alternator
Both relays can be removed if going mechanical or manually switched
The oil pressure sending unit has 3 wires going to it but only one controls the gauge. GM put a redundant circuit in there to override the fuel pump relay should it fail during driving. While it doesnt matter if its left in there, I usually remove the ORG and GRY wires to simplify the mess
Both power dist wires can be moved off of the starter to a power distribution block mounted anywhere in the engine bay. This cuts down on clutter and speeds troubleshooting when fusible links blow
Emissions common can be removed with no consequence. I opt to retain it since its a fused 12v source perfect for running HO2's
TCC can be removed for manual transmission cars
This is a bare bones setup I use on my race car
This is a 90-92 C100/C207 pinout
The C207 can be cut down to just 3 wires: speedo, MIL, park/neutral switch
The inj and PCM fuses will have to be moved
For TBI and older cars, you will have a VSS buffer box mounted under your dash. It is there because the PCM cannot understand the raw VSS signal and it must be broken down to something it can read. This is why the TBI cars run the VSS thru the C100 and V6/SD TPI cars run it directly to the ECM
Since the newer LS1/LT1/0411 PCM is quite capable of handling the VSS this box serves no purpose and must be wired around to get your speedo working
For correct speedo, run the VSS wires directly to the PCM, from there the PCM will output the correct 4,000PPM signal your speedo needs. It should go to pin D in the C207 then be connected to the green wire at the buffer box
Once I get a LS1/truck harness Ill write a how-to-swap it in to take the huge confusion out of most of the threads posted in here
Hey, my car was an auto but I'm swapping in a T56 if that makes any difference with my wiring harness you and I were talking about.
You will have to update your dash wiring for the new tranny just like any T56 swap
I posted about matching your tranny type to harness from the original car because to go manual you have to add pins to the C100. Ive never seen that successfully done short of buying a new C100
Nice write up! I think this might be the only thread dedicated to detailing harness work. I know I tried to take pics and make a write up when I did my harness, but I got so involved with it I soon forgot about pics and didnt even really take diligent notes like I intended.
This is GREAT info to help someone get started on their harness!!!
J.
__________________
ARE shortblock, Ross custom boost pistons, arp rod bolts, ARE ported oil pump,
MTI 2e 5.3L ported heads milled .030 with double springs,
228/224 113+1 Comp XE-R, Cloyes adjustable timing chain, LS6 valley cover,
fast 90mm intake, NW 90mm throttle body, SVO 30lb injectors, 85mm MAF,
ASP underdrive pulley, 160* t-stat, stainless LT headers 1.75" primaries
So is the harness you have for me from a T5 car or auto, or does it even matter since a T56 isn't a T5? When you say re-pinning the connector, is it just re-soldering the wires into the new positions on the new C100?
You will have to update your dash wiring for the new tranny just like any T56 swap
I posted about matching your tranny type to harness from the original car because to go manual you have to add pins to the C100. I've never seen that successfully done short of buying a new C100
Care to elaborate on that?? The only electrical connectors on the transmission are:
the reverse lockout,
the backup light switch,
CAGS
& the VSS output.
In my case, I've read that it won't be necessary to use one of the Dakota Digital boxes with the electronic speedometer in my GTA, as long as the ECM is tuned/programmed correctly - but I'd like to know for sure what you're referring to...
You need to build a new pigtail that runs from the rear of the engine down to the various trans connectors. These are contained in the swap harness, not the original
In addition to moving the connectors around for the new pedals, a few connectors may need to be swapped/added ex. clutch switch
Your auto dash harness will have none of this and using a T5 engine harness will send your backup lights (and VSS for TBI harnesses) to dead ends at the C100
You possibly could cut the C100 wires in question and move them to another pin use on the dash and engine side but in most swaps, ALL C100 pins are retained so you simply dont have any extra pins to move to
Post 145 begins the wiring with better pics
One difference i saw was he has a carb car so the ECM is not used. Most swaps reading about this wiring will have some sort of EFI which wants a park/neutral input
From his auto trans connector he leaves two wires off and simply wraps and forgets them. The ORG/BLK is the P/N wire from the PCM. The BLK/WHT is GRD
You need to build a new pigtail that runs from the rear of the engine down to the various trans connectors. These are contained in the swap harness, not the original
In addition to moving the connectors around for the new pedals, a few connectors may need to be swapped/added ex. clutch switch
Your auto dash harness will have none of this and using a T5 engine harness will send your backup lights (and VSS for TBI harnesses) to dead ends at the C100
You possibly could cut the C100 wires in question and move them to another pin use on the dash and engine side but in most swaps, ALL C100 pins are retained so you simply dont have any extra pins to move to
Make sense?
Yep, sure does. Thanks Pocket, I'd forgotten about the clutch switch...
In my case, I've read that it won't be necessary to use one of the Dakota Digital boxes with the electronic speedometer in my GTA, as long as the ECM is tuned/programmed correctly - but I'd like to know for sure what you're referring to...
Missed that part
All 3rd gen electric speedos that Ive seen require 4,000 PPM input. The best I can tell is LS1s use a 40 pulse per revolution input and change it to 4,000 PPM output to the speedo. The cruise output is 2,000PPM just like 3rd gen cruise
Regardless of older 3rd gens using a 2,000 or 4,000 PPM signal, the value can easily be changed when tuning the LS1 PCM to make what you have work
The dakota box is used to change LT1 T56 11/17 pulse per revolution signal to 2,000/4,000PPM 3rd gen signal when keeping the TPI
can u provide specific details on how u transfered the wires from the ls1 underhood fuse box to that tiny little one.
did u have to cut each wire ends and soder it to the caddilac box or do they just plug in.
What are you running with the two relays? Fuel pump and...? Fans? Do you have the "pink" wire items all running off of the ignition source (big pink wire) or do you have all of that powered from the battery via a relay?
Ide like to knock my fuse boxes down from 2 to 1... I sort of cleaned them up as best I could, but left everything in the stock f-body configuration to get the car running. Tried to avoid wire splices wherever possible.
Still good info in here! Im betting wiring scares a lot of people away from the LS swap...or makes them go carb'd.
What are you running with the two relays? Fuel pump and...? Fans? Do you have the "pink" wire items all running off of the ignition source (big pink wire) or do you have all of that powered from the battery via a relay?
Ide like to knock my fuse boxes down from 2 to 1... I sort of cleaned them up as best I could, but left everything in the stock f-body configuration to get the car running. Tried to avoid wire splices wherever possible.
Still good info in here! Im betting wiring scares a lot of people away from the LS swap...or makes them go carb'd.
J.
Fuel and fan, my TBI has a single fan
Everything but the HO2s are off the heavy pink IGN wire from the C100. INJ and PCM pinks are ran thru the mini fuse box. HO2s are off the emissions common
Quote:
Can you elaborate on cutting out the commons Pocket? Where to cut and what to do with the other ends exactly?
Common is where 3+ wires meet from the factory. Its under a black duct tape feeling wrap and has a long crimp with a dab of solder on it. They are about 3" long in most cases
I cut all the wires free just before and just after then discard the common. Most of the wires are either not reused or are rerouted requiring lengthening or trimming to fit with the new harness
In regard to your question about the one closest to the C100, it should be gray and have 3 wires to it. This is the fuel pump common. The relay output goes to the common which goes thru the C100 to the pump itself. This is all you need. The rest can be cut out of the circuit without issue
Care to elaborate on that?? The only electrical connectors on the transmission are:
Thanks Pocket, I'd forgotten about the clutch switch... 
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