Passing a power cable through the firewall on a 24 1500 - Very different than 2019-2023 models; seeking advice

[DubVBenz]

I have a 2024 GMC 1500 and I wanted to wire up a subwoofer behind the rear seats. I found great guidance on various forum posts and youtube that showed a unused grommet through the firewall that is intended for aftermarket cable routing (power/subwoofer or otherwise). It had a closed rubber nipple that you could cut off and fish a wire through there to the passenger side footwell.

 

So today I began the process to fish a power cable through my truck's firewall and found that it's completely different. There is no longer a passthrough grommet. I took out the battery (with much frustration ) and couldn't find a single place that I could see to get something through. I found a post online that I cannot seem to find again that stated the 2024s were completely different, and based off that description I think it's accurate. 

 

So does anyone have any guidance they can provide to get through the firewall without drilling? Looked very simple on videos for the 2019-2023s.

[DubVBenz]

Here's the one thread I previously found, on trailboss, so replace the URL because the **** mods apparently don't like competition. www.notrailboss.org/threads/firewall-grommet-change-in-the-2024-lt-trail-boss-for-power-wire.2109/

[dieselfan1]

There is a opening below the battery on the firewall. Looks like a plastic tube. It comes out below the lower glove box. 

[Velocity12]

I was in the same boat as you are. I had a 2019 Sierra and it had the closed grommet. My 2024 had nothing in the passenger side firewall like that. I just drilled a hole and put my own grommet, it’s tight around the wire so it kinda seals itself and it’s not in a spot that would let water through. 

[Chevyspeedster]

It's the same as before, just a little different as to where the nipple was. It's no longer easily seen from on the side of the grommet. They've moved it to the underside of the firewall passthrough wire harness. You can see it clearly underneath in the photo below.

Pic 1 is from the engine bay. You can see the channel where the wire will exit/enter the truck.

Pic 2 is from inside the truck and what is looks like if you peel the grommet back, which does not need to be done because then you'll need to replace the rubber around the grommet to around the plastic shroud which is not the easiest thing to do.

Just use an exacto #1 and cut a plus from the inside of the truck in the nipple. Pic one shows where the wire will exit.

Pic 3 shows a 4ga wire in it. It fits 4ga wire really well. No sure about 2 or 0... you may have to trim the nipple off then just make the plus/X cut bigger.

 

I also did not need to remove the battery to do any of this. Just work from mid engine with a ladder/step stool. Not the side of the truck.

 

Hope this helps a bit more.

 

Edited November 3, 2024 by Chevyspeedster

[bbmxta]

On 11/3/2024 at 1:52 AM, Chevyspeedster said:

Pic 2 is from inside the truck and what is looks like if you peel the grommet back, which does not need to be done because then you'll need to replace the rubber around the grommet to around the plastic shroud which is not the easiest thing to do.

Were you able to do this and it fit snuggly around plastic shroud?  Mine pulled away and there is only a 1/8" piece of plastic lip sticking out away from firewall so I see no way the grommet can snap back around it.  Just seems to sit loosely against firewall.