I have been blessed with a filled-in rear alarm keyhole from the previous owner.
I just bought one from Zip and was about to re-drill the hole based on the measurements in the AIM.
Boy am I glad I decided to measure the switch before cutting!! Unless it is not made per GM specs, it is quite a bit off from the AIM.... unless the AIM is wrong?



1.28\" Diameter mounting hole

.861\" Diameter mounting hole / ID

1.10\" OD

 

Looks like they used an escutcheon for those and then went to a smaller hole in 72
Check here, down near the bottom
https://www.corvetteforum.com/forums...uestion-2.html


M

 

Corvette central
56-71 56-67 Door / 70-71 Anti Theft Alarm Lock Bezel
Part #: 501086

M

 

I can always count on Mooser!
I read thru the thread you linked,, and apparently 72s went to a smaller size than 70-71, but they don't say what the size is. I even went thru the 1972 AIM and no info on the alarm whatsoever.
Now here's where it gets interesting; my car is a day 1 production, so if it's 1 thing I've learned over 10+ years of putting it back to "original", is that they opted to use 1971 parts wherever possible. Speedo, tach, all gauges, etc.

So, if I drill a smaller hole, then I shouldn't need the escutcheon, then it will be correct for a 1972. Is this correct
Or, get the escutcheon, drill the larger hole and it'll be correct for 1971 and most likely how my car came from the factory.

Geez this gives me a headache!

 

I'll check again tomorrow but my 72 AIM showed a 13/16 hole I believe. Not in the alarm section but I think it was with the other stuff, letters and such..... Maybe
Nope, the 13/16 was from a 69 AIM not the 72
Since the alarm was standard equipment that hole I guess was maybe already in the body so they didn't call it out on the AIM, same as the holes in the doors
M

 

That key switch you show is for a 1974 when the switch was in the left front fender it has the L shaped terminal that rested against the tamper switch

 

Kind of confusing
GM lists 2 (well 3) lock switches
The parts book says that used they used B&S locks P/N 3937671 for 68-69 but the vendors say 68-70 (so maybe 70E while they used up stock)


(the 68 AIM I have says the hole was only 13/16" ...)

Then there's mention of a P/N 3990870 being used for 71 - 74 and some vendors call out that number but there's no mention of it in the 1975 parts lists, I think it might be the part number for the "lock unit" which was the group of locks that were keyed alike for the car rather than an individual part number
The 1975 parts book does list a 3986860 as being replaced by the 374169 but I don't see anything linking 3986860 to the corvette and don't have any access to an earlier parts book than the 75 one

Then they list 374169 (1st design) listed for 70-77


After that it's a totally different thing all together

My guess is that they started using the "newer" small body switches in 70-71 and the holes were still larger so they needed to add that 3897449 Bezel / Escutcheon to make it work and then eliminated it sometime in 71 (in my 72 AIM there is a change to the lock group listed in March and another in Sept so maybe one of those was the removal of it)

ANYWAY
make the hole fit that lock body with the 4 square notches to orient it
M

 

Done! I still need to add the gasket in this pic, but the hole has been cut. 7/8" with 4 notches.

It's an optical illusion but it is in the correct spot. I could barely make out the outline of the original hole in the fiberglass.
Apparently it is not supposed to be centered in the CORVETTE logo.

 

Yeah the "V" in the corvette throws everything optically off to the right, damn monospacing
The gasket is same as the ones on every gm door lock out there so might be able to find one semi-easy
M

 

The alarm was standard on 72’s, in lieu of the fiberoptics of 68-71. Prior to that it was an extra-cost option. It’s clear that the hole for the alarm switch was not just drilled—it had to be punched in order to get the notches. I have seen original 71’s with a larger hole (using the bezel) and others with the smaller hole (not using the bezel). I’ve seen no rhyme nor reason for that. Two different fiberglass suppliers for that rear piece? 68-70 had the 1st style switch with smaller hole—were some of those leftover fiberglass pieces used in 71?
I clearly don’t have the answer.

 

Thanks all. I was about to loose my damn mind figuring this all out, as with everything on a 1st day production car. "If this, then that... except for Tuesdays, and in the month of May, and if you are wearing a black T-shirt".


Now, the $25,000 question... which leg of the tumbler gets the orange 12+volt wire? I would assume when you turn the key to the L to activate, that would be 12V.

 

Electrically it shouldn't matter and I can't help but think on the line it was whichever way the guy was holding it at the time as long as they installed it with the key teeth down.
(You could remove that extra leg section as well I guess)
M

 

Here are the 3 different styles that were used over the years

 

Yeah, mines that left one with the questionable part number (I think it might have been the 3986860 but couldn't find a document that said that) which was superseded by the right one 374169 which is the current replacement for all 70-77
I'd like to see a gm part catalog from around 71,72,73 to see what the actual part number was before the supersede
M

 

According to the judging manual, that center lock was used up to ~12,250 for 1970. After that it was the lock with the little swinging door for the key slot - which I assume are like those on the right and left. It also states cars are seen with and without the escutcheon with no further details.

 

I have a Oct 1970 parts book but i do not see the lock listed anywhere

 

Sounds like the previous owner did you a favor by filling that in for you (assuming he did a good job filling it and also safely dealt with the wires). I am probably going to start a flame war here, but I have to speak out in the event someone is contemplating doing something like this, and who will undoubtedly read this some day in the near or distant future. I will also preface the following with this, is my opinion, but very likely shared by others.

I think that alarm key mechanism is very unsightly - it's just downright ugly, ancient, gimmicky, and has no business on this vehicle. Unless you're going for absolute originality/collectors value in a L71, LS5, L88, or other rare/desirable optioned BB Corvette, and even the LT1 of the era, which is completely understandable, why bring it back? I have one on my '69 convertible, and can't WAIT to have it filled in when it gets repainted later this year. I doubt that will affect value of the car. In fact, it'll likely go up. haha. Mine isn't even functional, and I wouldn't use it anyway even if it did work. So I have to remember to go the back of the car and turn the key when I can just press a button if I want to disable the car alarm before I get in and drive? Easy enough to install a kill switch and/or alarm elsewhere (in a more convenient place) and out of site without that ugly thing ruining the fine @ss of the early C3 Corvette. Aesthetically speaking, the only place that would have been worse to put it on that car would have been the nose, over the flags.

That is the first thing that people see, besides the license plate, when behind the car. I'm all for originality, but not all of Chevrolet's ideas were good ones. There's a reason why they came up with the vastly improved VATS system on the C4s, as Corvettes were one of the top targets for thieves, with or without that keyhole on the back. At this point, anyone installing this primitive system is doing it for originality, and hopefully not looks, especially when there are more modern and vastly superior security mechanisms available that aren't based on 50+ year old technology. VATS wasn't perfect, but all you need to start the car is the key, and it sure beats an ugly keylock in a highly visible area.

Aside from bringing back originality to the above-mentioned more rare optioned early C3 Corvettes, this seems a fools errand, Anyone who likes that thing probably also likes big mudflaps, big mirrors, and a tall canopy, etc (or at least one of those) on their trucks that screams 'old man'. While there is nothing wrong with aging at all, we can age gracefully without shouting it from a mount top. The minute I get the repaint, that thing (and all its wires) are gone, and the hole filled up so folks can instead focus on that beautiful "C O R V E T T E" emblem on the tail.

 

Nice....
M

 

I've done my homework on this prior to going thru with it. It was an original item therefore it needs to be on the car. I have replaced every single wire on the car, every door switch and everything related to the alarm, gauges and T&T steering column rebuilt, new upholstery, etc.

Whether it's a bad design or how out dated it is, is totally irrelevant. It came with my car and so it belongs on my car. All 72's came with them from the factory.
Take the radio for instance, 2 ***** and push button selector switches: technology has come leaps & bounds since then,, but,, I choose to keep my original radio in the car despite how crappy it sounds.
Take the entire car for example. It is ENTIRELY outdated. Hand laid fiberglass body, inconsistent door gaps, poor fitting interior, etc. But I love it because it's mine to do whatever I want with, and if I choose to keep it all original, so be it.

 

Well, if that's your Corvette in your avatar pic, are you planning to remove the L-88 style hood too? That's not original to the car. And who cares about the radio anyway. It's a retro item that looks cool, but no better music than that V8.