1966 firewall question AC harness "hole"

[Joseph U.]

I am trying to restore a 1966 coup with AC.
There are two holes in the firewall. One is well visualized in the AIM (C60, E5 pg. F291) with a four hole configuration for the grommet. the holes seem to be for the Engine harness, oil pressure line, and two air lines. That picture also suggests that the AC harness goes thru the same hole as the engine harness. I don't see how this could possibly fit. there is a second hole in the firewall with a second grommet with two hole in it. this hole is on the slanted part of the firewall near the windshield washer motor. Could this be where the AC harness passes thru the firewall?
Just cant see how I can get both harnesses thru that one hole in the 4 hole grommet.
Does it really matter?
Thanks for the help.
Joe

[Scott S.]

Re: 1966 firewall question AC harness "hole"

I am trying to restore a 1966 coup with AC.
There are two holes in the firewall. One is well visualized in the AIM (C60, E5 pg. F291) with a four hole configuration for the grommet. the holes seem to be for the Engine harness, oil pressure line, and two air lines. That picture also suggests that the AC harness goes thru the same hole as the engine harness. I don't see how this could possibly fit. there is a second hole in the firewall with a second grommet with two hole in it. this hole is on the slanted part of the firewall near the windshield washer motor. Could this be where the AC harness passes thru the firewall?
Just cant see how I can get both harnesses thru that one hole in the 4 hole grommet.
Does it really matter?
Thanks for the help.
Joe

Joe,

If it's like everything else on these cars, then it probably matters

The second Grommet you reference is located on UPC 12-C3 (1-hole grommet) for 3spd. If yours is a 2-hole Grommet (for 4-speed), that one is called out on UPC M20/21/22-A4. With a 4spd, both the Tach and Speedo cables go through this Grommet on the slanted part of the firewall near the windshield washer motor. No room (or AIM instruction) for other cables, hoses or harnesses to go through that Grommet.

The engine bay side of the 4-hole grommet is shown on UPC 12-B2, showing the oil pressure pipe passing through the grommet, and also showing the Instrument Panel Harness Asm. passing through the grommet to connect with the Wiper Motor (also shown on the diagram you referenced, UPC C60-E5, and pictured again on C60-A2). So unless the drawing is wrong, it does appear that the Main Engine Harness (GM 6290155) and the Instrument Panel Harness (GM 2988869) both pass through the same large hole in the 4-hole grommet as shown on UPC C60-E5, with the oil pressure pipe and two vacuum hoses each going through separate holes.

Someone here who has C60 should be able to confirm this.

[John H.]

Re: 1966 firewall question AC harness "hole"

Joe,

If it's like everything else on these cars, then it probably matters

The second Grommet you reference is located on UPC 12-C3 (1-hole grommet) for 3spd. If yours is a 2-hole Grommet (for 4-speed), that one is called out on UPC M20/21/22-A4. With a 4spd, both the Tach and Speedo cables go through this Grommet on the slanted part of the firewall near the windshield washer motor. No room (or AIM instruction) for other cables, hoses or harnesses to go through that Grommet.

The engine bay side of the 4-hole grommet is shown on UPC 12-B2, showing the oil pressure pipe passing through the grommet, and also showing the Instrument Panel Harness Asm. passing through the grommet to connect with the Wiper Motor (also shown on the diagram you referenced, UPC C60-E5, and pictured again on C60-A2). So unless the drawing is wrong, it does appear that the Main Engine Harness (GM 6290155) and the Instrument Panel Harness (GM 2988869) both pass through the same large hole in the 4-hole grommet as shown on UPC C60-E5, with the oil pressure pipe and two vacuum hoses each going through separate holes.

Someone here who has C60 should be able to confirm this.

Scott -

I think the confusion here relates to the terminology used in the AIM describing the "harnesses" that pass through the 4-hole grommet, as there is no "engine harness" in that area - the "engine harness" is all forward of the firewall.

On a non-A/C car, the only wires passing through that 4-hole grommet are eight wires (from the instrument panel harness) that feed the wiper motor, washer pump, ballast resistor, and the backup light switch. On an A/C car, all of those wires remain, plus the "A/C harness", which has four wires from the plunger switch on top of the A/C box - three for the blower resistor, and one for the compressor clutch.

A/C only adds one 4-wire "harness" through that 4-hole grommet, and the "engine harness" isn't involved at all.

[Scott S.]

Re: 1966 firewall question AC harness "hole"

Scott -

I think the confusion here relates to the terminology used in the AIM describing the "harnesses" that pass through the 4-hole grommet, as there is no "engine harness" in that area - the "engine harness" is all forward of the firewall.

On a non-A/C car, the only wires passing through that 4-hole grommet are eight wires (from the instrument panel harness) that feed the wiper motor, washer pump, ballast resistor, and the backup light switch. On an A/C car, all of those wires remain, plus the "A/C harness", which has four wires from the plunger switch on top of the A/C box - three for the blower resistor, and one for the compressor clutch.

A/C only adds one 4-wire "harness" through that 4-hole grommet, and the "engine harness" isn't involved at all.

John,

Thank you for the explanation, it will definitely help when I'm ready to install the harnesses.