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2012 GMC Sierra Electrical Issues. NEED HELP!!


Jun 3, 2020
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Liberty Hill TX
I am having a serious mechanical/electrical problem and I really am at a loss of where to go. I pretty much tore my truck apart to put new carpet and utility lighting throughout. In doing so, I was trying to go through the main grommet in the firewall with an exacto and it must have hit something. I pulled back and the tip of the exacto was black and bent. Unfortunately, I had the positive of the battery disconnected and not the negative. So I am thinking that I grounded something out. Now, the horn, ac/heater blower, and an airbag notification is on. I checked all the fuses I could find. It looks like they are all intact. I really need some guidance as to what I should do next. Should I replace all of the relays and fuses anyway? Reset the computer? I am truly at a loss and I'm really pissed at myself for putting myself in this position. Let me know what your thoughts are and THANK YOU SO MUCH IN ADVANCE!!!
It was the main wiring harness. Any suggestions on how to get in there without too many difficulties? Thanks for responding!
I am having a lot of issues getting the "bonnet" off of the main wiring harness. I am thinking about cutting it away to be able to get to the wires and them taping it back up securely. Any help/advice would be appreciated.
I will get you a picture in just a bit.

The reason why I said "bonnet" is because there is this black think covering all the wires. If there is a grommet it's the strongest one I have ever seen. I can't push it in or out!
Here is the picture

Never saw one like that but yes you'll have to find whatever you shorted out and get it fixed. Your saying it burnt the knife? If that's the case you'll likely be doing more than taping up some wires. Looks like that boot would push back into the cab, I'm only guessing though.

Curious... you said you removed the positive cable yet you burnt a knife, it had to be getting a positive somewhere to do that?
You need to check the air bag code and see if there is any codes in the HVAC. I would start there
Hope this was not a new truck still under warranty. But it maybe time to go talk to a mechanic at the dealership. Guess they are service technicians today. Most will help if they can. It got put into metal some how. There has to be a way to get it out.
It's not a new truck. 2012. I'm giving it one last shot and going to get under the dash and see if I can't get some leeway from that end. Maybe tidy everything up a little better. I don't want to do something halfway. If I can't get it by then, it will have to go into the doc. Thanks for all of the feedback!!