LML firewall grommet, wiring access? - Chevy and GMC Duramax Diesel Forum
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post #1 of 5 (permalink) Old 04-21-2019, 02:28 PM Thread Starter
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LML firewall grommet, wiring access?

I am trying to hook an egt probe to my Insight CTS and cannot find good access through the firewall. Where are guys running the probe wire through?

Looks like there is a grommet behind this box but I cannot get it off. Feels like no matter what I do something is going to break if I pull on it.

Spent about an hour pulling the fender liner, tapping the manifold, installing the probe, and putting everything back together. Now Iíve probably spent an hour trying to get the wire into the cab with no luck. WTH???
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2011 GMC Sierra 2500 LML only mod is an Airdog II 4G100 lift pump with an Edge Insight CTS2.
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post #2 of 5 (permalink) Old 04-21-2019, 04:28 PM Thread Starter
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Well I managed to get that grommet out and ran my probe wire through it without removing the black cover pictured. Everything is put back together and working.

I would still like to know how the black cover comes off if anyone knows.

2011 GMC Sierra 2500 LML only mod is an Airdog II 4G100 lift pump with an Edge Insight CTS2.
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post #3 of 5 (permalink) Old 04-21-2019, 06:14 PM
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i dont know if you have enough slack but i typically use the parking brake cable grommet under the floorboard on the drivers side
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post #4 of 5 (permalink) Old 04-22-2019, 08:48 AM
J83
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Originally Posted by E92FF View Post
Well I managed to get that grommet out and ran my probe wire through it without removing the black cover pictured. Everything is put back together and working.

I would still like to know how the black cover comes off if anyone knows.
The center round peg you see is a Christmas tree clip, you need to pull that out to get the cover off. Though, removing the cover does not get you a ton more space, it still a pretty lousy wire run on the new trucks. Easiest way is to use a slightly pointed (but not sharp, you dont want to pierce wires) piece of stiff wire, like an old car antenna, and poke it through the boot from the engine bay, pull a wire through the firewall from inside the cab, connect your wire to that wire, lube it up and pull it back through.

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Originally Posted by GM4ever View Post
i dont know if you have enough slack but i typically use the parking brake cable grommet under the floorboard on the drivers side

^^ that is also an option, as is the hood release grommet, though both of those are only for smaller wires, anything over 14 gauge should probably go through the main firewall boot so you dont pinch the wire too much.
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2015 Chevy Silverado 2500 HD 6.6L LML
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Last edited by J83; 04-22-2019 at 08:50 AM.
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post #5 of 5 (permalink) Old 04-22-2019, 09:00 AM
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That big plastic cover just snaps in place. You won't hurt it. Just pull it off and you can get to the big firewall grommet. I have a bunch of wires running through there.
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2011 Chevy Silverado 2500HD CCSB 4X4
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