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Options for fixing jagged opening in firewall?

1K views 23 replies 13 participants last post by  69StangRestomod 
#1 ·
Working on the '66 Fastback I rescued from its several-year hibernation in a carport of the woman who inherited it from the original owner and I've found a few issues with the wiring.

Apparently a previous owner had a problem with an ignition wire and decided to just rout around the main under dash harness (using a piece of heater hose as a wire wrap) but not before hacking up the sheetmetal hole in the firewall where the dash harness connects to the headlight harness.

Aside from not wanting to have jagged metal vibrating against the wiring harness when replaced, I'd like to properly seal up the hole a bit.

Is the only way to repair properly to cutout the hole and weld in a new piece of metal? I'm not a welder, so any good non-welding options/ideas would be appreciated.

Thanks in advance. The wealth of experience and generosity is what makes the Mustang community so great.
 

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#3 ·
If you don't want to weld it then I'd say the next best option would be to make a cover plate for it and sheetmetal screw it or bolt it in place. You could drill a hole and install a grommet and run the wires through it.
 
#4 ·
Did the jackleg hacker actually cut away any metal? Maybe he just rolled the metal back and if you remove the wires you can hammer the rolled edge back into place. Of course the metal is now stretched and shrinking it to fit back in place will require the skills of a knowledgeable metal man.
 
#5 ·
I sympathize with the lack of welding skills. But don't let that prevent you from having the repair done properly. Get on the phone and start calling welding shops until you find one that will make a house call , or let you make an appointment to come in and have them do the job while you wait. The cost is not going to break the bank, and you will have the satisfaction in knowing you didn't take the easy way out by having a haphazard repair done.

Z
 
#8 ·
I'd get a body section. Those plugs are major PITA to fit (at least for me) and I would want the exact size hole back there.

I like the idea to use a donor section and sheet metal screws, It would be easy to make look like a custom job for access rather than a bodge.

For your wiring I would use Randy at Midlife. He does a very reasonable rebuild of your factory harness

Cheers. Peter
 
#9 ·
Use a file to smooth out the edges of the current hole.
Then cut a new piece of sheet metal with the right sized hole in the middle and with about 1/2" overlap on the top & bottom and maybe 1/4" on the sides.
Put some sealer on the edges (silicone or seam sealer works well) of the new piece and rivet it on top & bottom to the firewall. Put the new piece in from the backside so you won't see the overlapping piece on the engine bay side.

When the sealer is dry, hit it with a matching spraypaint and it will barely be noticeable.
 
#10 ·
Clean up the area to bare metal and remove any sharp or rough edges. Fashion a "repair plate" with the correct sized rectangular hole for the firewall plug large enough for a 3/4 inch overlap with the existing metal all around. Affix the repair plate with automotive panel adhesive and when cured apply seam sealer and paint.

As anal as I am, I'd open the existing "butchered" hole to an exact dimension, all around, larger than the final hole... example, if the final hole is 1 inch x 2 inches, then make the hole in the firewall 2 inches by 3 inches, cut the repair piece 2-3/4 inches x 3-3/4 inches and flange the outside edge all around by slightly less than 3/4 inch, affix it from the inside, with panel adhesive, so that it's flush with the exterior of the firewall, then fill the small gap with AllMetal, sand and paint, for an invisible (from the outside, anyway) repair.
 
#14 ·
^^^^^^^^^

For all the people that are OK with a non welded fix, I have one question for y'all;

Why do you think it's called a firewall ?

Answer: it's supposed to keep an engine bay fire isolated to the engine compartment. Keep it from spreading to the passenger compartment.

There's no epoxied or riveted fix that's going to contain a fire as well as a welded fix. Aside from the safety issue, there's also the case of unibody stiffness. A welded fix maintains the unibody integrity and strength. Any other fix does not.

It's one thing to be satisfied with shade tree fixes on your car. But in my view it's irresponsible to use the forum to advise a novice to repair his car in an manner that leaves it less safe.

Z
 
#15 · (Edited)
Even if you cut out a plate and attach it, I would put some nice looking stainless button head metal screws in the plate to attach it and not rivets. I would also round the corners of the patch plate so it looks a bit more professional. It will still be a patched over hole but it should look nice. You can probably live with that for a while or quite a while until you decide later to completely clean up and restore your engine bay. That area is not very visible with everything installed in the engine bay but you will always know it is there. To punch out the rectangular hole for the wiring harness plug, you can start by drilling the whole line with a small drill bit and then use a dremel to finish the cut out and clean it up. Tedious but it will work.

However, if this is your time for cleaning up and restoring the engine bay, that should be properly welded and fixed permanently now. If you clean up your hole, cut your fill plate and take the edges of the hole and the plate down to clean bare metal for welding, you can find a shop with a mig and it doesn't have to be a metal fab shop. Most of the general purpose vehicle shops around where I live have a mig welder and could stitch up something like this in less than an hour. They shouldn't charge a lot for sticking a pre-prepped, cut to size plate. If you go this way you will also want to take down the perimeter of this area to clean metal on the inside so you don't catch something on fire under there.

I did option #1 with some holes in my floor pan and lived with that for a long time when I was drag racing my car. I cut back the rusted out holes to squares or rectangles and laid in new floor pan over the top. It looked ok inside but was ugly under the car. Now, I have the whole front of my car stripped and have been going back and welding everything properly. It looks a whole lot nicer from the under side even though I am about the only person who will ever see it.

I am still not done with this. I have had every other mechanical thing that I own break down or tear up multiple times since I started on this part of the mustang. The mustang hasn't been rolled out of my shop now for some 3 months while I have had 15 different mechanical situations to fix on other stuff. I am not happy about it but my truck, my bike and my lawn mower have to run and I fix everything myself. I am about to see the light at the end of this tunnel though and hopefully I will be finished with the last patch SOON. I just hope the light at the end of this particular tunnel is not an oncoming train, LOL.

Good luck, which ever way you go with it.
 
#20 ·
Thanks again for all the replies. If I could get my hands on a MIG welder, anyone want to guess how much "practice" it might take before a novice like me could get a patch panel stitched into place well enough for the repair to not be noticeable?
 
#21 ·
I watched dozens of you tube videos on mig welding and then spend 2 or 3 afternoons practicing on sheet metal pieces and old license plates. The first project I did was I built my own welder cart with my new welder and it came out ok. I had already been welding with a stick though but I'm not sure how much that really helped. I still can not consistently make "pretty" welds but I keep trying.
 
#22 ·
Now is a good time to re-route the wiring harness and hide it. Along the outer fender well is a good spot.
Then fiber glass a patch over the hole (under the dash)...when it sets up....fill in (inside the engine bay side) with bondo and sand smooth. No welding involved!!
You'll be surprised how much "cleaner/uncluttered" it will look under the hood.
In fact do ALL the wiring under the hood the same way!! Great custom idea anybody with a little patience can perform.
6sally6
 
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