Tangled up in an LS factory harness

[shearjs]

Hey guys,

I know this is a common topic of discussion and I've tried to do as much research as possible, but still feel a little confused at the moment. Over the wkend I have spent several hours working my way through my factory harness of a 2004 DBW Silverado 2500 lq4. I plan on keeping the drive by wire and using the 4l80e trans that came stock in the truck. I got lucky on my initial purchase and got the engine, trans, harness, computer, tac, and pedal all from the same vehicle, so that shouldn't be an issue I have to overcome at a later date. I've been following the info from LT1swap.com, like most people have done, and have come to a roadblock that leads to a couple of questions. At this point, I've stripped all the mess away to expose the wires, and pulled the unneeded pins from the blue and green pcm connectors. I've worked my way through the C2 connector that goes to the factory fuse box, and labeled all the pink (12 volt switched +) wires according to the pin outs on LT1. ( http://www.lt1swap.com/vortec_truck_pinouts/2004.htm ) I still have two main plugs located near the C2 plug that I am unsure about. One plug is gray, and I believe it attaches to the TAC module. The other plug is black, and has a couple wires that were de-pinned while working through the pcm connectors earlier. Does this black plug get removed?? If so, what happens to the wires that go from the black plug to the plug that attaches to the TAC module?? Also, at this point, should I separate the pink wires for the 12v switch + into groups to be fused, based on their specific applications: injectors, coils, etc.?? Thanks in advance for you help.

Gray Connector...to the TAC?


Black Connector...?

[usmcchevy]

Grey connector goes to the TAC. Black connector I can't tell, where do all the wires its attached to go?

I ended up with 7 fuses on my harness. I know Lt1swap only shows 4, but I didn't intergrate any circuits and everything in my harness is wired to the same amp fuse it was designed to use.

This is just a pic of my notes, never intended on posting this so hope you can read it . The dots represent the fuses and all the things down the left side are the circuits that need power.

[shearjs]

Thanks usmcchevy for the reply. Great job on your build too by the way! One of these days I need to take the time to start my own build thread. I like the way you broke all your fused circuits out into groups. I'll probably try to do something similar to that once I get that far along. I can't remember off the top of my head where any of the wires in the black plug run to, but I'm planning on tracing them down this afternoon after work to see what I can figure out. I initially thought it was the C100 connector, but I'm not 100% sure on that either. Hopefully soon I'll have some of this ironed out. I appreciate the help!

[RocketKing]

Can you get a pic of the black plug?

[shearjs]

I took a few minutes and traced the wires from the black plug to see where each went. I'm not exactly sure how they are labeled but I have numbered them 1-16 with 1 being the top left, and 16 being the bottom right.


1 - BLUE - ALT PLUG? 3 WIRES - BLUE, BROWN, GRAY
(BROWN - #15 GREEN PCM - CHARGE AND CONTROL)
(GRAY - #75 GREEN PCM - ALTERNATOR FIELD DUTY CYCLE)
2 - WHT - #10 GREEN PCM - ENGINE SPEED SIGNAL
3 - GRY - TAC (GRAY) PLUG
4 - YLW - #59 BLUE PCM - CLASS 2 SERIAL DATA
5 - OPEN
6 - BLUE - GOES T A SECTION THAT WAS CUT FROM THE YARD.
7 - OPEN
8 - GRY/BLK - TAC (GRAY) PLUG
9 - GRN -#58 BLUE PCM - CLASS 2 SERIAL DATA
10 - BRN/WHT - #46 GREEN PCM - MIL CONTROL (CHECK ENGINE)
11 - PNK/WHT - #38 BLUE PCM - DAMPING LIFT/DIVE SIGNAL
12 - OPEN
13 - GRN/WHT - #50 GREEN PCM - VSS OUT 4K/MILE
14 - BROWN - GOES TO A SECTION THAT WAS CUT FROM THE YARD.
15 - OPEN
16 - BLUE - TAC (GRAY) PLUG

The first picture shows the plug, but I took it upside down for some strange reason. The number would start with number 1 at the bottom right, with 16 being at the top left. Hopefully this isn't too confusing. Thanks guys.

[TR65]

Just a suggestion that worked for me. Buy the GM service manual for the vehicle and year model that the engine and harness came from. Then you know exactly where each wire goes and what it does. And you have all the diagnostic procedures for trouble shooting.

Good luck,

TR

[usmcchevy]

My harness didn't have that connector, but just by looking at the signals, it would have went inside the cab.

1, no idea
2, run your tach off this one
3, Cruise control
4, serial data for your OBDII port
6, ??
8, Cruise
9 same as 4 i believe
10, provides ground for check engine light
11, ??
13, Speedo sig
14,??
16 Cruise control

Only way to know for sure is to do as TR said or find someone with Alldata and print off the wiring diagram. Hope this helps a little.

[shearjs]

Originally Posted by tr65

Just a suggestion that worked for me. Buy the GM service manual for the vehicle and year model that the engine and harness came from. Then you know exactly where each wire goes and what it does. And you have all the diagnostic procedures for trouble shooting.

Good luck,

TR

I think you have the right idea. Is there a particular place that you guys like to get the service manual from or would a yearly subscription from alldata for the particular vehicle be a better idea?


I decided to send an email to Brendan at LT1SWAP since I was following his info on my harness. Below is what he had to say.

Most if not all of those pins, are a direct link to the YELLOW wires that I listed to REMOVE from the PCM or BLUE to keep for external connection. Since you don’t have the mating connecter, I usually CUT those all off. As I get to the highlighted YELLOW wires at the PCM, I will completely remove them from the harness. Most of the time they go to one of the three plugs about 12” down from the computer. The TAC module has some pins going there too for cruise control hookups. The BLUE wire from alternator, not sure why some vehicles have it. I usually cut the blue wire an inch or two from the alternator plug, and remove the wire, taping over the blue and combining it with the other two from alt, brown and gray.

Gray plug should be tac module. It has a few pins going to the plugs shown, these are for crusie control hook ups. There is a link to DBW Cruise Control info off my main vortec 5.3/6.0 page.

-Brendan


Seems to be simple enough. Hopefully this will help someone else out that may run into this issue in the future. Thanks for all your help.

[TR65]

Jason,

I buy from Helm Inc. online. They print the factory service manuals for GM.

I also have bought used service manuals on ebay.

Only the GM Factory service manuals will do.

There are some really cheap sources online for downloadable service manuals but I don't know if they are complete or if they are the real thing.

TR

[shearjs]

Thanks TR. I'll check it out. Sounds like it would be a good investment.

[mcbassin]

Jason,
You are almost exactly where I am at on my harness modification. I feel like I missed something on the LT1 site. I looked all over for where to go after all the un-needed wires are removed. I finally gave up and went on to something I could do (install the motor and tranny in my frame). I am getting ready to get back on the wiring pretty soon. I'm interested in what you end up doing with these connectors. I have just about the same vintage engine too.
I wish there was a step by step manual to get through this process. I would pay for it. Wiring is my biggest weakness. Sometimes I think about buying an aftermarket harness just to avoid this exact situation.
Ben (USMCchevy) has a ton of knowledge and has helped me a bunch on my swap.

[usmcchevy]

Mcbassin, Don't give me too much credit, I only know enough to be dangerous

Seriously, all I know came form boards like this and basic electronics knowledge.

[mcbassin]

Originally Posted by usmcchevy

Seriously, all I know came form boards like this and basic electronics knowledge.

Oh, I see the problem I lack this

[shearjs]

I've been away from home quite a bit here lately so my progress on the harness has kind of came to a stand still at the moment. I did get my connectors, relays and such in last week to wire up my fuseblock so I need to get back into it soon before I forget where I was at. I ended up getting rid of the black plug and setting wires aside that I'll need for cruise control and such as LT1swap stated. As soon as I get back into things I'll post some more info and pictures on the progress.

Mcbassin and usmcchevy, I've followed both of your builds for a while now, and they've both been very helpful in choosing the path I want to go and helping me get there. My work on the truck has been so spread out that I've tried to hold off on creating a build thread until I have enough worth posting, in hopes of not boring everyone to death. Thanks for your help guys. Much appreciated.

[shearjs]

It's hard to believe I posted this stuff over a year ago, and I'm just now getting around to finishing up my wiring harness. With any luck, I hope to try an initial startup in a couple weeks.

usmcchevy, if you're still subscribed to this thread, I noticed that you have 3 relays as opposed to 2 that Brendan shows on LT1Swap. Is your third relay for your starter?

[faribran]

just wanted you guys to know that all the things you are going thru helps others... even if no one says so.......
i have just started my ls1 engine in my 56 Bel Air....... i bought a harness, but plan to do my own next time....
keep it up.. we all learn with you guys..