Hey guys I am really close to doing my swap and had a question about wiring harness' to use. Is it better to get a premade wiring harness from a company or better to get the original harness for ur car cut down by a local shop that you know does a good job. I have my harness already and know a shop that cuts them down for a good price, I was just wondering if there is advantage of either selection. Thanks in advance guys.

 

The real question here is do you want to take a chance on a wiring harness failure leaving you high 'n dry when you least can afford it. Personally, I would buy an aftermarket harness from a reputable firm rather than build my own or have a shop do it for me.

The amount of testing required for a rebuilt harness is time consuming. It's not merely cutting 'n splicing wires to make the harness fit. You need to measure the resistance before and after to make sure you aren't setting yourself up for a future failure down the road. Many old, stock harnesses I've seen are too far gone in terms of wear 'n tear to even consider modifying. However, it's your money so the choice is up to you. If you go the shop route, ask for a couple of references on past harness work to check on the quality of their past work.

Good luck!

 

By the way I love your site name, thats so cool to me! The local shop I am considering I actually know the owner, he is really experienced with ls conversions. He has been doing them for years and has a flawless reputation. I was really asking because I wanted to know is there an advantage either way. If its the same I may just have him do my current harness.

 

It depends on who you talk to. An aftermarket harness manufacturer will tell you buy new and someone who mods harnesses will tell you to do the mod.

The real answer is, if the harness is uncut and you can live with the length then there is no reason not to get a modified harness from a reputable supplier.

However to really answer your question in an unbiased fashion we need to know more info like:

1. What year and model is the donor vehicle/engine?

2. Where do you want to mount the PCM?

3. Are you keeping the engine just as it came out of the donor or are you
changing the intake/injectors and alternator?

Regards,

Ken Wolkens

 

I modified my own harness, because I wanted to familiarize myself with the whole process. And to say I did it. But I would also never try to start from scratch on a homemade harness.

 

Ken the donor vehicle is a 99 camaro ss

I am not sure what the pcm is in the first place but I would like my engine bay as clean and neat as possible.

The intake injectors and alternator are the same, the motor has had a cam kit put in it (springs, lifters, pushrods, cam, timing chain, and upgrades oil pump) Thanks for any and all help ken.



I was told by my installed that the draw back of the modified stock harness is you dont get a fuse box, with the psi harness you get a fuse box in case there are any electrical issues down the line.

 

The 99 had it's PCM on the RH side in the corner where the fender and cowl came together. That will allow you to place the PCM in about the same place in your car.

As for a fusebox, yes, they should always be used.

 

Aftermarket harness is usually easier, but can cost a little more, and you are left with a harness routed the way the vendor chose to route it... which may or may not be the same as you want it routed. If you are very picky about how your wiring it routed or how it will look on the finished install, then you have to find a vendor harness that meets your needs, find a local guy who can do it for you, or do it your self.

I reworked the stock harness (only had 17K miles on it) mainly because no one makes a harness for my application (LS4/F40 in a Fiero) and I wanted total control over how it was routed and how much of it was visible in the engine bay. I did it the hard way...
Started with this:


Did this to it:


Finished product:

 

Very very nice. Do you have a build thread?

 

Or it can be untangled like mine without cutting like this:



Each connector can then be routed as you want it to it's destination.

 

if you have the cash and dont mind spending it buy already made harness.. if your tight on funds and dont mind the risk modify!!but you still need a fuse box of some sort

 

This is more of a summary one:
https://ls1tech.com/forums/conversio...peed-swap.html

This one has everything:
http://www.fiero.nl/forum/Forum3/HTML/000123.html


For clarification, I unpinned every wire at the ecm, I didn't cut many wires except where I eliminated a few connectors.

 

Now that you say it I can see where you did unpin the ECM connectors. It was the TCM pigtail that threw me off.

That's a lot of work...

 

I looked at my swap this way. I could spend xxx amount for a harness ( going rate is between $450- $550). I could sell my old harness ( and did for $275.00). Now if you keep your old harness you have probably 20 hours work into it ( give or take) to redo your old harness. It is still a old harness ( say your donor is a 2000 camaro, so it's a 13 year old harness that could be britle and might have corrosion on it). For the extra $250.00 you have a harness that is new and only needs 5 or 6 wires ( say 4-5 hours) to make it work for your vehicle. I'd go with new over used if I had to choose on it.