Finish Wiring of a Stand Alone Harness
 

I've gotten good feedback from this forum as I'm working on my swap. My next dilemma is the wiring. I've read thru several different threads, trying to compare others issue with mine. I'm not trying to cut corners but I also have a budget and don't want to spend if I don't have to on an area.

The guy I bought my motor/trans from does pull-outs and modifies the harness before selling them.

I've had people tell me to just buy a plug and play harness and I would, if my harness wasn't already rewired as a stand alone.

The motor was fired up before I loaded in the truck and I was given a schematic to complete the wiring. The wiring was run to be able to mount the PCM and TAC module under the dash.

My problem is I've never done wiring but I'd really like to learn and try and tackle this myself.

Below is a picture of how the wires were bundled into (2) bundles (power supply and accessories)

Attachment 1820238

And below is a breakdown of the wires that I have in each bundle.

Attachment 1820258

I was trying to find examples of how to complete the harness and looked around the web and LT1swap.com and found a video on youtube with a diagram that really helped explain how to wire a fuse block and relays. My only issue is that some of the wires used in the diagram don't match what I have in my harness (see below).

Attachment 1820262

Can anybody help me with this?

Re: Finish Wiring of a Stand Alone Harness
 

Here's the 1st picture

Attachment 1820264

Re: Finish Wiring of a Stand Alone Harness
 

LT1swap is harness help line tons of information , im in the middle of harness rework now.

Re: Finish Wiring of a Stand Alone Harness
 

Easiest thing to remember; if its pink, it needs power.

Literally, swaps have been delayed longer than needed because we simply forgot to find another pink wire and put it to 12v

Re: Finish Wiring of a Stand Alone Harness
 

I was trying to match the diagram from LT1swap.com for wiring my fuse block/relays/connector but there's a couple wires missing from my bundle. With me not having any knowledge on wiring, I can follow step by step instructions, but I don't want to experiment or learn a hard lesson if I wire something wrong.

I know all I need is a fuse block and relays, however I'm not sure how to go about wiring that up with the wires in my modified harness.

Re: Finish Wiring of a Stand Alone Harness
 

Check out Brendan from LT1swap you tube videos. They're long but he walks you through reworking a harness. I watched it several times before doing mine. had minimal issues.

Re: Finish Wiring of a Stand Alone Harness
 

quick question, what year is your harness and pcm?

Re: Finish Wiring of a Stand Alone Harness
 

What I keep finding is the the same info, such as taking a stock harness and making it a stand alone harness. The info I need is once that is done and the wires you need are broken out and separated, then what?

I found a helpful video on YouTube from UCanDoIt2, he used info from LT1Swap to make a diagram of the fuse box with relays. They don't mention what size fuses to use and where wires go after that.

I know I'm having issues because I've never tackled wiring until this project, so it's quite the project to learn wiring on.

I can't find much information on the accessory wires either, such as TCC wire, VSS and NSS wires. If I can figure out how to do it, then I'd love to document the wiring and add it to my build thread.

Re: Finish Wiring of a Stand Alone Harness
 

My whole setup came out of an '03 Envoy. When I purchased my combo it came with TAC module, PCM (obviously), MAF sensor and gas pedal (since my setup is a DBW.

Re: Finish Wiring of a Stand Alone Harness
 

I get the exact same donor, im following this now. so your pcm plug ins are blue and green then?

Re: Finish Wiring of a Stand Alone Harness
 

Yes I believe so, to be honest I haven't taken apart the PCM. The wiring harness was modified by the seller and taped/loomed up with unnecessary wires removed already.

I've been researching the harnesses since I purchased my motor. LT1Swap.com has quite a bit of info about the breakdown of motors from vehicles.

Have you read thru that website yet?

Re: Finish Wiring of a Stand Alone Harness
 

What exactly is it you're looking for? It's going to be a little difficult to tell exactly what you're working with since someone has already done some mods to the harness, but not impossible. The wires in your pic you posted that I can see says '12V + Key' should be pink wires, but the guy used red, this may trip people up. Anyway, TCC gets hooked to the brake switch, the VSS goes to your electric speedometer and the NSS isn't really necessary on a swap unless you just want to use it. If you have a specific question it will be easier to answer, so maybe take it a few wires at a time, that should make it easier on you.

Re: Finish Wiring of a Stand Alone Harness
 

Sorry LS1, this wiring layout is messing with my head. You're right, I need to ask specific questions in order to try and get answers.

In my OG post, I posted 2 pics...1 picture was my harness layout and the 2nd was an example I was trying to use to build my fuse block.

I know that both orange wires (battery 12v+) and red wires (ignition 12v+) need to be run on a 15 amp fuse. I'm trying to determine how to go about actually wiring it up that way, can I model the 2nd pic diagram of the fuse block/relays as an example? Meaning do I run each wire into a different fuse location (4 fuses, 4 wires)?

I'm hoping someone could help me create a diagram using the wires I have, then I could wire them accordingly.

Again, I have no experience wiring, which is why I need to ask so many questions...I don't want something wired wrong. If I have step by step instructions, I could go from there, but to make connections on my own, I don't want to attempt that.

Re: Finish Wiring of a Stand Alone Harness
 

Ok, I see. I didn't realize the first pic was a diagram of the harness you have. So basically you would wire it up like the second pic, at least the fuse block part, on the right side. Only difference would be you will only have 2 ignition fuses rather than the 3 in that pic. The other things will go to what ever they are for, MIL will go to the check engine light, TCC will go to the brake switch, etc.

Re: Finish Wiring of a Stand Alone Harness
 

I forgot to mention that I went and purchased the same Dorman fuse block and (2) 40 amp relays, plus the 8 pin connectors shown in my 1st post. I like the way it's clean and detailed...no loose wires, everything has a place, I like that idea.

Also I've been ordering wire (20g for the misc connections, 16g orange for the fuse block, 12g purple for the starter connection, 12g red for the battery to fuse block connection and 10g black for the ground from battery to body). I still need to get my battery cables and battery.

Re: Finish Wiring of a Stand Alone Harness
 

LS1, do you have an email that I could contact you regarding wiring questions?

Re: Finish Wiring of a Stand Alone Harness
 

hello 19SIKtySix. I hope all is well. i tried to hit you up on IG but you are private. from the pics i saw, doing the harness is pretty much cut and dry. oh, yeah, i've done this before. dm me your number and i call you to explain anything to help you out. Listen to LS1nova71, he's a god when it comes to LSx swaps. in a few of my own swaps, i put the stock harness, with no wires removed, on the engine and tranny, plug up a vats deleted pcm, wired my fuel pump, grounded the block, frame, engine, added 12v+ power/Ingniton and fire the motor up. of course i added fuel and connected the starter, but its easy.

Re: Finish Wiring of a Stand Alone Harness
 

Hey Dec010974, sorry about the IG thing, send me a request and we can connect on there.

As I've mentioned, I working with a modified harness already, I just need help with how to finalize the the fuses/relays and get this thing fired up. I feel confident in the seller's ability to modify harnesses. He sells swaps all the time and wires them this way on all of them, plus his personal vehicle.

Because of my lack of knowledge with anything auto electrical, I wouldn't know where to start. However, if there's a diagram or something visual that I can see, it'll help me tons.

Re: Finish Wiring of a Stand Alone Harness
 

Hey 19SIKtySix, how did you make out with your wiring? Hoping you can pass on what you learned.

Re: Finish Wiring of a Stand Alone Harness
 

Good morning bigmoe, what item(s) are you needing help with?

I actually have my engine wired up and running now. dec010974 (who is a member on here) had me contact him and he helped me a ton with sorting out the wiring.

As I mentioned before, the wiring harness was modified by the seller of my motor/trans. He supplied me with a schematic for the harness and also labeled all the wires.

I had dec010974 wire me up a LS fuse block to have fuses and relays for my swap. He walked me thru which wires connected to my existing wiring harness and what to test.

I'm sure you could reach out to him and ask him questions or post them on here and I'll try to help the best I can.

Keep us posted on your progress!

Re: Finish Wiring of a Stand Alone Harness
 

I'm on hold while my truck is away at paint for the next several months. I have the stock engine harness I'm going to rework. I have instructions for the fuse block to add to the end of the new harness. I'm just trying to wrap my head around the rest of the engine compartment. My 65 is bare. I need to buy a main wiring harness to wire the whole truck - lights, dash, most of it no big deal, just pondering about the engine compartment because some of the original wiring will not be needed with the LS engine harness replacing it? Starting at the battery and where to go first. Starter? Do I need a main fuse/junction? Where to come off of to feed the main fuse box. Voltage regulator? or is there one built in to the LS alternator? Neutral safety switch? Some of the stuff I'm pondering.

Re: Finish Wiring of a Stand Alone Harness
 

bigmoe - I can share some insight as to how we did my dad's 64 and answer a few of your questions from last night. My dad's 64 has a new American Autowire classic update harness which replaces all wiring the wiring on your truck, so don't worry about reusing anything. The autowire kit has pretty good instructions and if I remember correctly the power for the autowire harness comes from the starter and/or the LS batter tap (a red box with a cover next to the alternator). The autowire harness has its own fuse block. I'm doing a swap with a 6.0 out of an 04 Escalade and I deleted the NSS because from what I've read it's not necessary. Someone can correct me if I'm wrong, but its purpose is to tell the computer which gear the transmission is in so it won't start in neutral as the primary safety reason. It also controls the idle (will idle down when shifted from park into gear). With the autowire harness and if you have a steering column with a built in neutral switch, it will prevent the engine from starting while in gear or neutral. We retrofitted a repro 67-72 automatic column and it came with the switch. Since the autowire harness is made to work with a carbureted engine, it will have wiring that you won't need - such as the distributor wiring and VSS (vehicle speed sensor - comes from LS harness). But you can use the coolant temp sensor, oil pressure sensor, and brake warning switch wires from the autowire harness to run to your LS sensors.

The harness from his LS was reworked by Speartech (back when they were doing reworks). The rework basically involved deleting the downstream 02 sensors and other emissions, coolant level sensor, and a couple other plugs that aren't used in a swap. What Speartech provided us was a reworked harness with a fuse block and relays that look just like the setup from LT1Swap. My dad recognized that the classic update harness has a few circuits for modern upgrades such as power seats, power locks, power windows, etc. What we did was test these circuits to determine which were constant hot and which were switched hot and used those spare circuits to power the LS harness and eliminated the extra fuse block and relays.

I don't know if you're reworking your harness or not, but LT1Swap is definitely the best resource I know of. It's totally doable, even if you don't have a lot of wiring experience. I started by laying out my harness on a sheet of masonite and arranged the wiring as it lays on the engine and drilled holes in the masonite (like Ucandoit2 on youtube) and zip tied it down in a bunch of spots (not tight so you can pull wires through them, just to hold them in place). From there, I pulled all the loom and tape off. Using the pinout charts from LT1Swap, I confirmed each wire with its correlating sensor/plug to confirm it's not needed and pulled them out one by one. It is as simple as cutting all the pinks and oranges from the LS fuse block and then merging them so you don't have 20 wires to connect to your power source. After you've removed all the wires you don't need and inspected the remaining wires for damage, I would recommend testing each one to make sure there is continuity by using a tester set to continuity mode and touching one lead to the pin at the PCM connector and the other end to the pin on the corresponding plug. If you really want to go the extra mile, you can layout the harness (after removing unneeded wiring and plugs) on the engine, plug everything in, and reroute the wiring so that you can mount the PCM inside the cab to keep it out of the elements and make a cleaner engine bay. It's not necessary, but I'm in the middle of it right now and think it's worth the time.

Reworking the harness is not something you'll get done in a day. It takes time, it's very detailed, and it shouldn't be rushed. I've spent a couple hours on mine in the evenings when I have time and I've enjoyed it. An LS harness is not complicated, it's just a bunch of wires to keep straight. Take your time, label everything, and take notes of what changes you make so you can reference later if you run into any issues.

Re: Finish Wiring of a Stand Alone Harness
 

I 2nd LT1swap. Rebuilt my harness using his website and you tube videos. Def the best resource I found!!

Re: Finish Wiring of a Stand Alone Harness
 

Hope this helps some.

Re: Finish Wiring of a Stand Alone Harness
 

Guys, thanks so much for the advice. I'm sure I'll get it figured out. Now if the painter would just get through his part, lol.