Firewall Grommet questions

Discussion in 'The Big Chill' started by 72 goat herder, Oct 7, 2020.

  1. 72 goat herder

    72 goat herder Well-Known Member

    Car: 1972 GS Stage 1 with Auto Trans and A/C.
    I have some holes in the firewall that I need some help understanding what they are for and if they need grommets. I have added some pictures to better describe my questions.
    1) There is a small hole to the right of the voltage Regulator. What is this hole for?
    2) There is a 1.75" hole to the right of the Blower Motor Relay. I believe this hole is for the wiring for the A/C controls in the dash, coming from the engine bay. I believe this hole uses the 1.75", single hole grommet. Can anyone confirm?
    3) What is the square hole to the right of the throttle cable for?
    4) Do I need the 3 hole (2.25" diameter) grommet that is used for A/C vacuum lines? If so, where does this grommet go? (I don't have any 2.25" holes in the firewall).

    Thanks in advance for your replies and knowledge! Slide1.JPG Slide2.JPG Slide3.JPG
  2. Utah455

    Utah455 Well-Known Member

    Here are a few pics of mine that I’m restoring. Car is a 70.

    The hole to the right of the regulator is for the rubber push grommet from that is for the firewall pad.


    The large hole uses the 3 hole AC grommet for the AC extra harness and vacuum lines. The brown wire is the tach wire. It’s not suppose to go there since my car didn’t come with a tach. Just in case I want to add a tach, the wire is there.


    I have to remember what I bought for The square hole by the throttle cable. I believe I got it from Ames Pontiac. Possible called kicked down cable grommet. It was a plastic piece that just pressed into the hole.

    This should be what I bought.

    Last edited: Oct 7, 2020
  3. 72 goat herder

    72 goat herder Well-Known Member


    Thanks for the response and pics. Strange thing is, the hole I have in my firewall is 1.75". so that would drive me toward the single hole 1.75" grommet. The 3 hole grommet (like your picture) is 2.25". This is the ad description: 3 HOLE FIREWALL GROMMET WITH METAL CORE 2" (MOUNTS IN THE MIDDLE OF FIREWALL ON CARS WITH A/C & ALLOWS THE VACUUM LINES TO PASS THROUGH IT. HAS A RUBBER COATED STEEL CORE. IT IS 2 1/4" IN DIAMETER). So, I am concerned that the larger 3 hole grommet won't fit in the 1.75" hole.

    My quandary continues.

    The rubber push grommet for the firewall pad makes sense - thanks for that pic.
  4. Smartin

    Smartin Staff Member

    The 3 hole grommet has 3 metal prongs that fit inside the 1.75" hole
  5. 72 goat herder

    72 goat herder Well-Known Member

    Ah, thanks Smartin. That makes sense.

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