They both accomplish the same things the same way. It's just wiring and signals and voltage. One wire is no better than the other.
The fact that an aftermarket company makes it doesn't make it perform any better however, they can make it fit your application better physically and without extra wires that aren't being used.
Aftermarket harnesses are generally easier to install and figure out since everything is labeled and it comes with instructions, whereas with a stock harness, you have to figure everything out. But everything is basically a one-off plug, so even that isn't very difficult. The difficulty arises when trying to figure out which wires are needed and which aren't and which ones need to be adapted to the car the harness is going into.

I know on an LT1 harness, there are only a few wires that connect the harness to the car.
12v hot all the time
12v with ignition
VSS signal - to speedo
PNP signal - to park/reverse switch
Tach wire - to tach
Oil pressure wire - to gauge
Water temp wire - to gauge
Ground - to ground
Fan signal - to fan relay
Fuel pump signal - to fuel pump relay

The rest either go to a sensor on the engine/tranny, to a plug into the pcm, or to the ODBII diagnostic port.

If you take time to study and familiarize yourself with a schematic, which you really should do if you are swapping an efi engine, the rest is just work.

Basically what you're paying for in an aftermarket harness is the labor and materials to build it, not a performance upgrade.

 

Thank for the info! With the stock harness and PCM, is a seperate controller and harness needed in order to run a 4L60E?

 

If the 5.3 had a 4l60e originally, then no separate controller is needed. The transmission harness is an extension of the engine harness.

 

I ve used several of them. The latest was nice, and was $350.....from a guy in prescott AZ.

Search craigs list in az and I think Hell turn up, or pm me.

Time is worth something.

 

This is who I used, hell of alot cheaper then some of these companies out there. High quality wiring and have had no issues. You should give him a call his name is Robert.
www.ls1wiringharness.com Sometimes he does e-bay auctions his store name is fuelinjectionconnection

 

orale cabron, animate!!!!

 

Why did you completely dis-assemble your harness? It' easier just to remove the wires from your PCM connectors that you don't need and back-pull them out of the existing tree structure. It will save you tons of time and not have birds nest.

 

That's actually what I did at first, and kept the stock fuse boxes etc. I'm mounting the PCM inside the car so I needed to change the layout of the harness. The placement of the 02 sensors and changing the location of the coils was a part of it as well. You can see the coil harness hanging off to the side in the 2nd pic.

I'm going to mount the PCM on the inside of the car and run the loom through the firewall.

It's actually not that bad.

This is what I removed

some of the interior harness and the engine bay harness



I'll post pics of the other stuff I pulled out tomorrow.

 

i just got mine in the mail from ls1wiringharness.com $500.00 it looks real nice comes with relays for fans and fuel pump and a fuse pannel all wires are labeled you wont be dissapointed i will try to post pics later

 

"orale cabron, animate!!!"

Undalay*

I like how you did that and it looks very clean. I want to try this out cause keeping the extra $500 would be nice.