Anyone Know What This Hole's For? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Moreyel** · 05-10-2020, 11:56 PM

Getting ready to install my wiring harness for a TBI system. Found this hole with what looks like a factory grommet, but nothing going through it. Located under the heater box. Sorry, one of the pics is sideways. This is a factory A/C 72 Blazer that I don't remember ever seeing or taking anything out of. I'm asking cause if nothing important goes there, then I'll enlarge it some and use it for my TBI. Thanks

70LonghornCST · 05-11-2020, 06:02 AM

Not a definitive answer to your question, but I am thinking that may be for the heater blower motor wire? If so, I think it has a grommet that needs to be installed first, then the wires feed through. I don't have my truck here, so I can't go out to double check. I'll look tomorrow, but I'm sure that others will chime in.

**DeadheadNM** · 05-11-2020, 07:55 AM

I don’t see a similar hole on my firewall.

**Moreyel** · 05-11-2020, 10:41 AM

Thanks for the answers. It looks factory but it's hard to tell. It's about 3/4", so more than one wire went through. Looks like I've got my starter hole for the harness. I just need to get in there today to make sure a passenger foot won't be able to damage it.

**paul mora** · 05-11-2020, 10:46 AM

If it is on the bottom someone my have done that to identify any leaks in the heating system

mister.freeze · 05-11-2020, 10:46 AM

I don't have THAT hole on y 72 CST. I have a different one, on the opposite side. Don't know what it WAS for though, using it for my MSD. First pic is from the engine bay, second is from the passenger seat. Sorry, mine are sideways too.

**Moreyel** · 05-11-2020, 10:48 AM

Maybe. At first I thought it could've been some kind of drain. But, there's nothing there TO drain. So, you might be right.

**DeadheadNM** · 05-11-2020, 10:58 AM

It does appear factory being flared slightly. Interestingly, the holes for tachometer harnesses and auxiliary battery harnesses are also 3/4".

**Moreyel** · 05-11-2020, 11:10 AM

Yeah Pete. But this is kinda low.

**DeadheadNM** · 05-11-2020, 11:26 AM

You bet. Just to clarify, I'm not suggesting this hole was for either of those harnesses, which are placed on the opposite side of the firewall near the fuse block.

**Moreyel** · 05-11-2020, 11:43 AM

I know. Looks like it may have been added on.

05-10-2020, 11:56 PM	#1
Moreyel Active Member Join Date: Jun 2013 Location: Cedar Crest, NM Posts: 197	Anyone Know What This Hole's For? Getting ready to install my wiring harness for a TBI system. Found this hole with what looks like a factory grommet, but nothing going through it. Located under the heater box. Sorry, one of the pics is sideways. This is a factory A/C 72 Blazer that I don't remember ever seeing or taking anything out of. I'm asking cause if nothing important goes there, then I'll enlarge it some and use it for my TBI. Thanks Attached Images __________________ 72 Blazer, 70 El Camino SS, Anniversary HD FatBoy, 2012 Ram 3500 4WD Dually, 17 Dodge Challenger, 80 Vette, 65 Chevy 3/4 Ton 4 W/D Pickup and some more. Wife: 06 GMC Duramax 3500 4WD Single Wheel, 2016 BMW X3. Next: Rust removal on my Blazer. Thinking of putting a 50 Chevy cab on a 76 Chev 4 WD pickup. Members Met: Aldtime, DeadheadNM

05-11-2020, 06:02 AM	#2
70LonghornCST Moderator Join Date: Jun 2008 Location: Modesto, CA Posts: 5,775	Re: Anyone Know What This Hole's For? Not a definitive answer to your question, but I am thinking that may be for the heater blower motor wire? If so, I think it has a grommet that needs to be installed first, then the wires feed through. I don't have my truck here, so I can't go out to double check. I'll look tomorrow, but I'm sure that others will chime in. __________________ 2018 Chevy Crew Cab 2006 Impala SS 1965 Plymouth Sport Fury 1970 Chevy Longhorn Bucket Seats Shoulder Belts Front Tow Hooks Factory Air Factory Speedwarning, Tach & Vaccum Factory Tilt CST Package AM/FM Radio Bumper Guards Richard 70 Longhorn CST Build Adding an AM/FM Decal

05-11-2020, 07:55 AM	#3
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,320	Re: Anyone Know What This Hole's For? I don’t see a similar hole on my firewall. __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

05-11-2020, 10:41 AM	#4
Moreyel Active Member Join Date: Jun 2013 Location: Cedar Crest, NM Posts: 197	Re: Anyone Know What This Hole's For? Thanks for the answers. It looks factory but it's hard to tell. It's about 3/4", so more than one wire went through. Looks like I've got my starter hole for the harness. I just need to get in there today to make sure a passenger foot won't be able to damage it. __________________ 72 Blazer, 70 El Camino SS, Anniversary HD FatBoy, 2012 Ram 3500 4WD Dually, 17 Dodge Challenger, 80 Vette, 65 Chevy 3/4 Ton 4 W/D Pickup and some more. Wife: 06 GMC Duramax 3500 4WD Single Wheel, 2016 BMW X3. Next: Rust removal on my Blazer. Thinking of putting a 50 Chevy cab on a 76 Chev 4 WD pickup. Members Met: Aldtime, DeadheadNM

05-11-2020, 10:46 AM	#5
paul mora Senior Member Join Date: Jan 2009 Location: huntington beach california Posts: 976	Re: Anyone Know What This Hole's For? If it is on the bottom someone my have done that to identify any leaks in the heating system __________________ Pulatoy

05-11-2020, 10:46 AM	#6
mister.freeze Registered User Join Date: Dec 2003 Location: Houston, TX Posts: 734	Re: Anyone Know What This Hole's For? I don't have THAT hole on y 72 CST. I have a different one, on the opposite side. Don't know what it WAS for though, using it for my MSD. First pic is from the engine bay, second is from the passenger seat. Sorry, mine are sideways too. Attached Images __________________ '72 K5, known as 'the Fox.'

05-11-2020, 10:48 AM	#7
Moreyel Active Member Join Date: Jun 2013 Location: Cedar Crest, NM Posts: 197	Re: Anyone Know What This Hole's For? Maybe. At first I thought it could've been some kind of drain. But, there's nothing there TO drain. So, you might be right. __________________ 72 Blazer, 70 El Camino SS, Anniversary HD FatBoy, 2012 Ram 3500 4WD Dually, 17 Dodge Challenger, 80 Vette, 65 Chevy 3/4 Ton 4 W/D Pickup and some more. Wife: 06 GMC Duramax 3500 4WD Single Wheel, 2016 BMW X3. Next: Rust removal on my Blazer. Thinking of putting a 50 Chevy cab on a 76 Chev 4 WD pickup. Members Met: Aldtime, DeadheadNM

05-11-2020, 10:58 AM	#8
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,320	Re: Anyone Know What This Hole's For? It does appear factory being flared slightly. Interestingly, the holes for tachometer harnesses and auxiliary battery harnesses are also 3/4". __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

05-11-2020, 11:10 AM	#9
Moreyel Active Member Join Date: Jun 2013 Location: Cedar Crest, NM Posts: 197	Re: Anyone Know What This Hole's For? Yeah Pete. But this is kinda low. __________________ 72 Blazer, 70 El Camino SS, Anniversary HD FatBoy, 2012 Ram 3500 4WD Dually, 17 Dodge Challenger, 80 Vette, 65 Chevy 3/4 Ton 4 W/D Pickup and some more. Wife: 06 GMC Duramax 3500 4WD Single Wheel, 2016 BMW X3. Next: Rust removal on my Blazer. Thinking of putting a 50 Chevy cab on a 76 Chev 4 WD pickup. Members Met: Aldtime, DeadheadNM

05-11-2020, 11:26 AM	#10
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,320	Re: Anyone Know What This Hole's For? You bet. Just to clarify, I'm not suggesting this hole was for either of those harnesses, which are placed on the opposite side of the firewall near the fuse block. __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

05-11-2020, 11:43 AM	#11
Moreyel Active Member Join Date: Jun 2013 Location: Cedar Crest, NM Posts: 197	Re: Anyone Know What This Hole's For? I know. Looks like it may have been added on. __________________ 72 Blazer, 70 El Camino SS, Anniversary HD FatBoy, 2012 Ram 3500 4WD Dually, 17 Dodge Challenger, 80 Vette, 65 Chevy 3/4 Ton 4 W/D Pickup and some more. Wife: 06 GMC Duramax 3500 4WD Single Wheel, 2016 BMW X3. Next: Rust removal on my Blazer. Thinking of putting a 50 Chevy cab on a 76 Chev 4 WD pickup. Members Met: Aldtime, DeadheadNM



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