Topic: 1970 - please help identify proper firewall body plug

[Cobrajet428]

The car is a 1970 Mach 1, 428CJ 4-spd, Dearborn-built 10/69.

There is a hole in the firewall located just above and to the right of where the main wire harness comes through, and just above and to the left of where the throttle cable comes through. I measured the HOLE to be approx. 15/16" diameter, and from a photo I have of another car I can see there should be a body plug installed there. Note this is NOT the big hole in the center of the vertical part of the cowl area, but below the pinchweld on the firewall. It's a little hard to see with the shock tower braces installed.

When I installed all the body plugs from my kit some years back, there was no plug that was the right size for this hole. I have looked at the Ford assembly manuals and shop manuals and can't find a drawing that shows this hole/plug. I believe (from photos) that it may not be present on '69 cars, only '70s.

Could someone help me identify this plug? I'd really like to fill the hole properly. A part # (visible on the face of the plug), hole size measurement (to verify that mine hasn't been enlarged), and especially if you have an extra you can sell me would be fantastic!

Here's a photo of what I'm talking about - you can see firewall insulation behind the hole that's missing the plug (the shock tower brace has been removed):

[joe747]

THERE ARE TWO SMALL HOSES THAT GO THRU THAT HOLE TO A MODULE UNDER THE DASH I THINK THAT THE RIBBER PLUG HAS A HOLE THRU THE CENTER OF IT .WILL SEE IF I HAVE ONE TO GIVE YOU A PART NUMBER

[Cobrajet428]

Aha... I believe I've seen that in the drawing for the 1970 Distributor Modulator system. That wasn't used on a 428CJ as far as I know, just the 302 and 351C. I've seen the system on a friend's 351C-4V car some years ago. That explains the hole being unique to '70. I would think for this application it would use a standard body plug, as there would be no need to pass anything through the hole, unless you or someone else here knows differently.

A photo of someone's firewall (Boss 302 or 428CJ or other without modulator) showing this area would be very helpful.

[Cobrajet428]

... and the correct answer is:

It's a standard body plug 377949-S.

It turns out my car which has a 15/16" diameter hole, required a 377678-S plug, not the 377949-S that another '70 428CJ car had installed. The 377949-S was fall-out loose when installed. I was never able to confirm the normal size of this hole, and mine looked "factory" so thought I'd just post this information in case someone else runs into the same situation (no plug for this hole) and needs a part number.

Measure the hole - if it's smaller than 15/16" it's probably going to need the 377949-S, if 15/16" you'll need the 377678-S as that fits perfectly.

Big thanks to Andrew at MagMustangs for the help locating and supplying me with plugs.