Topic: Extra 70 Dearborn firewall Hole

[Big Al]

My Dearborn, Aug '69 built Mach (w A/C) has an "extra" slotted, punched hole in the middle of the firewall.  i have noted the hole "outline" on others, but they weren't knocked out (see 70 Dearborn Firewall Holes thread dated 12/07/2020).  Mine doesn't appear to have been used or plugged (which may explain the rusted front floors).  What should i do in this case?  plug? (with what?) or is there a use I'm not aware of?
Thanks in advance for your help
Allen

[J_Speegle]

That GIANT washer is suppose to cover that slotted hole. Don't use the posted picture for other details

On non-AC cars that hole is not fully stamped or punched out and does not need a plug or seal




More pictures of the hardware and close-ups. Tossed a non-AC picture in there for others and since it uses different retaining hardware from the AC applications for the standard heater. That plant and year

[specialed]

Al  70  dont use the rear engine ground cable since engine grounds on neg cable tab by voltage regulator bolt below starter solinoid.

[Big Al]

Houston - we have a problem.....  attached are two pics taken during disassembly (I understand someone could have added or changed in the fifty yrs since the car was built, but pics are better than my memory and what was there,,,,IS a very good indicator), but the slotted hole is shown "open" and unused and the heater blower mount is shown then, in the same position it is currently placed.  Also please note Jay, that the blower mount won't work in the slotted hole without reworking the firewall mount of the cabin blower assembly (why would i rework the mount??, the inside components fit perfectly as mounted currently).  If i did move the mount and use the slotted hole, then I'd have the hole used now to plug or something.  (Yes, Marti report indicates, its a factory A/C car)
Also note that a firewall ground was present during dis-assembly, and i was always told..... "Put back what you find.... unless......"  but this would be an easy fix to remove. 
So at this point, I'm considering making a metal blank and replacing the "slug".   I'd still appreciate anyone weighing in on this still   ...... I have thick skin (Texan) and appreciate the opinions of those that have put some thought into their reply.   
thanks again, Allen

[specialed]

Al  what was the ford ID # on the ground cable that was on your car that u removed? The  new cable u installed is small block longer c8zb  68-69 big block used shorter c8wb cable. Do u have a 70 marti battey cable set and if so look at the negitive cable design for the tab with bolt hole by front v-regulator top bolt hole. Did your car have the original negitive cable and was it installed correctly grounding the engine?

[Big Al]

Ed  -  The "original" cable is toast.  Most of the wire is exposed because the insulation is hard and falls off.  So the firewall cable ground in the photo is now gone (banned to Island of Misfit and Unwanted parts)  and i'll use KM's cables as the ground.  thanks for catching it.   Allen