Help with engine wiring harness

[jkking72]

I have a 2012 GMC Sierra 1500 5.3L V8. Unfortunately, I was attempting to go through the firewall and hit several wires and it has become a huge mess. Long story short, after mechanic bills and other issues, I have to replace the wiring harness. My question is this, all of the wiring harnesses I see only go up to the fuse box. I need the wiring that goes through the firewall and up through the dash. Is this called something different or am I just not seeing it when I am trying to find an engine wiring harness? I hope I'm explaining this correctly, if not, please feel free to comment. Thanks so much!!

[Sharpz]

you can search here, but if you are looking for the complete wiring harness for all of your dash, that is a lot of wires, you might try a pull a part place.  Also you can search here for what you are looking for specificly.  I didnt know your details so just chose one. https://www.wholesalegmpartsonline.com/cars/Chevrolet/2012/Silverado--CREW-CAB-LTZ/Wiring-Harness/Silverado--CREW-CAB-LTZ-parts.html

[Brian715]

That sounds like quite the ordeal. Without seeing it, I would call it the body harness. How many wires were severed that a competent mechanic can't repair a few broken wires? If they can't do that, no way I would let them attempt to tear the whole dash apart and replace a body harness. 

[slj2008]

check your dealership ( parts man ) , get a print out of what you need . Buy New or repair your self ?? good luck.

[jkking72]

There are several burnt and melted wires at the site where the wires insert at the firewall. If there are more wires affected from shorts, I have no idea. I have a towing, stabilitrak, and airbag light on. I took it to a mechanic and after almost $700, it now has a battery drain and nothing is fixed. 

[Sharpz]

13 hours ago, jkking72 said:

There are several burnt and melted wires at the site where the wires insert at the firewall. If there are more wires affected from shorts, I have no idea. I have a towing, stabilitrak, and airbag light on. I took it to a mechanic and after almost $700, it now has a battery drain and nothing is fixed. 

yeah that is a huge issue then. You need to completely remove all of the dash, and probably the duct system to access all of these wires to remove and feed in the harness's that you are speaking about.  A heads up, if you were to just change the heater core and no wires, I believe the book says 8 hrs, so don't expect this to be a  few hour project.  Again what I would suggest is getting the wires from a pull a part, but first remove the dash, and anything else preventing you from seeing the wires completely before just replacing blindly.  Make sure you disconnect your battery too, leaving it hooked can cause a fire, or even more damage even if the truck isnt running. 

[jkking72]

Is there any way to get to these wires to repair them other than pulling everything out (pulling the wiring in through the firewall into the dash to get a good look at it)? When I attempted repair prior, I pulled it through to the hood and really couldn't get at what I was trying to repair. I'm just wondering if this might be worth a shot before doing a complete dash teardown. 

[jkking72]

On 3/7/2021 at 8:33 AM, Brian715 said:

That sounds like quite the ordeal. Without seeing it, I would call it the body harness. How many wires were severed that a competent mechanic can't repair a few broken wires? If they can't do that, no way I would let them attempt to tear the whole dash apart and replace a body harness. 

I told them what was wrong and they replaced the steering wheel sensor, with me telling them what the problem was. They even brought in a "specialist" and he couldn't figure it out. I saved up money to take it to the shop only for it to come out worse. The guy told me literally to put a picture up over the warning lights and not worry about it! I now have this serious battery drain that I didn't have before so I don't know what they have done. I'm not made of money and I'm disabled so it's very difficult for me to get in and out of places like under a dash. I'm just so frustrated with the whole thing! I'm the most irritated at myself for cutting the wires in the first place!

[Brian715]

That sucks for sure. Hope you can get it sorted out

[It's Tim]

That sounds like it goes way beyond replacing just a couple of wires. By the time you've figured out how many and what components actually got torched you would probably be much farther ahead just buying something else. There have been late model vehicles incorrectly "jump started" and were deemed a total loss afterwards.

Best of luck.

[Sharpz]

6 hours ago, jkking72 said:

Is there any way to get to these wires to repair them other than pulling everything out (pulling the wiring in through the firewall into the dash to get a good look at it)? When I attempted repair prior, I pulled it through to the hood and really couldn't get at what I was trying to repair. I'm just wondering if this might be worth a shot before doing a complete dash teardown. 

no there sure isnt.  Here is the problem and why you have no choice but to strip the dash to inspect all of your wires. You don't know what wires were affected and which ones were not. Just because you replace one or two doesnt mean there isnt 20 more that are damaged.  Sometimes one breeds the other, and wires can burn long amounts of coating/insulation, and can get so hot they can melt other wires too.  You are very lucky, that 1) your truck didnt catch fire, and 2) that it didnt fry major electrical components of your truck.  Disconnect the battery as I said, Park this one, and remove the dash and probably the duct system. It isnt easy by any means, but that is where you are at.  It doesnt cost you any money to remove the dash but will be extremely costly every time you start that pig up, and melt more wires, fry your brain, bcm, ecm, etc.  Removing the dash will allow you to visually  inspect all of your harness wires, and who knows,  maybe you can just splice in a few tape them up and be done, but at this point probably not.  Its hard to image what one hole drilled in the wrong spot can do, but here you are.  Not to kick you why you are down either, but cutting short cuts or at least trying to is what got you here in the first, place, dont cut corners with this. Make sure you fix it right, or you might be plagued with problems down the road. 

[jkking72]

I really appreciate your honesty and completely understand/agree with what you are saying. I am so frustrated with myself for this entire situation. So many things I wish I would have done different. I do have a friend who has offered help and she has over 10 years in auto restoration. I'm thinking this will be my spring/summer project. Not exactly how I wanted to spend my summer, but I do love my truck. As far as parking her for a while, are there any precautions I need to do with the gas and tires? I have pretty expensive tires and sure don't want to lose those. The reason I ask is because I am disabled and it takes me a lot longer to do things than most as my back doesn't move very well. So this could actually take me awhile to complete. 

[Sharpz]

you could jack stand/block your truck up, and keep the tires in the garage, if that isnt an option,  contractor bags over them and taped will keep the sun from messing with them too bad. Jack it up once a month and rotate 90 degrees, and they will be fine. Fuel stabilizer is about all you can do for the fuel, hopefully you use no ethanol.  Something to do, if possible, is make good labels for what came from where and what order, filming your friend take the dash out, would be helpful putting it back together.  It isnt horrible to be honest, but time consuming.  There are plenty of videos out there on how to remove the dash, and what you need to do that.  Just make sure y'all are  thorough,  Make this a one time deal.  Good luck, and please be sure to post the updates, and questions, there are plenty of people that can help answer your questions.

[jkking72]

@Sharpz

You really have given me some great advice and I can't thank you enough for your honesty and helpfulness. I will definitely keep things up to date and do it the right way this time! Thanks again!!