Testing 1972 Alarm System

[Phil D.]

The alarm system was disconnected at the key switch when we got this car so we've reconnected the wires. If I turn the key to the right to set the alarm and remove the key, the alarm system still does function. I've tested the door and hood switches and they work fine and I know the horn will sound and the flasher will make it go beep, beep, beep, etc. The key switch however only makes momentary connectivity about 1/8 turn through the 1/4 turn range and has no connectivity when turned fully clockwise. If I leave the key turned to exactly that spot where it has connectivity, then the alarm sounds almost immediately and continues sounding even tho the doors and hood are still closed. I don't know if the key switch is faulty or the relay or both. Can anyone provide insight into how the alarm system works and how to test these components?

[Harmon C.]

Re: Testing 1972 Alarm System

I would say one of the switches is not adjusted correctly. The key switch may need contact cleaner.

[Robert S.]

Re: Testing 1972 Alarm System

I have repaired the alarm system on both mine and my son's 74' and in both cases it was corrosion of the key switch internal contacts that was causing the problem. I suspect you have a similar issue. Remove the switch wires from the key switch and with a door open short the wires together. If the alarm goes off then you know it is the switch. I do not think you can disassemble the switch so you are looking at replacing the switch. Note: I cleaned my switches in a chemical solution without disassembly to get them working but it was not a long lasting solution.

[Phil D.]

Re: Testing 1972 Alarm System

Note: I cleaned my switches in a chemical solution without disassembly to get them working but it was not a long lasting solution.

Local locksmith said he could take it apart, but there was risk of damaging the cap so its worth a try first. What solution specifically?

[Robert S.]

Re: Testing 1972 Alarm System

I did this several years ago but my maintenance records said I used a liquid solution of two parts white ammonia mixed with one part hydrogen peroxide. I mixed up a small amount in a glass jar and put the switch into the mixture for about twenty minutes as I recall. I then rinsed the switch in water and blew it dry with compressed air. I used a VOM before and after to check the switch and found it was good after the dunking in the solution. I tested the solution beforehand by dunking an old oxidized brass bolt and it came out shiny clean. Give it a try and report your results.

[Gary B.]

Re: Testing 1972 Alarm System

Local locksmith said he could take it apart, but there was risk of damaging the cap so its worth a try first. What solution specifically?

Phil,

While the alarm switch/lock can be opened up, that requires the stainless steel face cap be removed by prying up the 360 degree crimp on the back side. I think you'll find that there is no replacement face cap for alarm switches. So the locksmith will undoubtably use some mechanical process to re-crimp the original face cap once the internals have been restored. If he's careful with the face cap, it can look OK from the front side, but not from the back. But that won't matter, if he's careful enough not to create any damage to the front side while de-crimping and re-crimoing. One can do something similar to repair faulty door locks, but in that case people use a replacement face cap that has 4 tabs that are bent over on the back side.

If you search long enough, and you are lucky, you might be able to find an NOS D keyway alarm switch, in which case the easiest thing to do would be to recode the storage compartment lock and tire lock to match the new alarm switch. The last alarm switch that GM sold, now discontinued, had the H keyway, so most NOS switches you find these days won't have the necessary D keyway for '72. But you might get lucky and find a D.

Gary

[Phil D.]

Re: Testing 1972 Alarm System

I did this several years ago but my maintenance records said I used a liquid solution of two parts white ammonia mixed with one part hydrogen peroxide.

Thanks. Can I assume this mixture was made using the aqueous solutions of 10% ammonium hydroxide and 3% hydrogen peroxide commonly found at the local hardware and drug store? Don't want to blow myself up in a junior chemistry set explosion.

[Robert S.]

Re: Testing 1972 Alarm System

I can't answer your question specifically. As I recall I bought the white ammonia in the cleaning aisle of a supermarket and a small bottle of hydrogen peroxide at a drug store. Both are liquids and I mixed them by volume. I do not believe that mixing these two chemicals is in any way dangerous. There is no obvious reaction when the two are mixed together.

[Phil D.]

Re: Testing 1972 Alarm System

Thanks. Will try it this weekend. Hopefully it will work. If not then will move on to seeking a replacement.

[Michael G.]

Re: Testing 1972 Alarm System

Phil, If you do go the replacement route and can acquire the proper coded replacement, there really isn't any need for a locksmith. I have done this procedure and it only requires a ton of patience. Just be sure to de-crimp the cap evenly around it's entirety. Uncrimp only to the point that it needs to be "popped" off. Put in the key, pull out the tumbler bar and swap out with the new replacement's tumbler bar. New switch with original key. The re-capping is just a matter of protecting the caps face while slowly rolling back the crimp. I will not call it "easy" but I would nervous that a hired locksmith might not want to apply the patience and time it would take to do without leaving any evidence.

[Phil D.]

Re: Testing 1972 Alarm System

Phil, If you do go the replacement route and can acquire the proper coded replacement, there really isn't any need for a locksmith. I have done this procedure and it only requires a ton of patience. Just be sure to de-crimp the cap evenly around it's entirety. Uncrimp only to the point that it needs to be "popped" off. Put in the key, pull out the tumbler bar and swap out with the new replacement's tumbler bar. New switch with original key. The re-capping is just a matter of protecting the caps face while slowly rolling back the crimp. I will not call it "easy" but I would nervous that a hired locksmith might not want to apply the patience and time it would take to do without leaving any evidence.

Awesome! Thanks. I was going to be a little anxious about that as the couple of replacements we've found so far, the sellers want a lot of money for them. I feel a little better about maybe trying that now but fingers crossed that the soaking solution works.

[Gary B.]

Re: Testing 1972 Alarm System

Awesome! Thanks. I was going to be a little anxious about that as the couple of replacements we've found so far, the sellers want a lot of money for them. I feel a little better about maybe trying that now but fingers crossed that the soaking solution works.

Phil,

It's not unreasonable that these alarm switches are no longer inexpensive or easy to find. According to my records, these were GM-discontinued more than 7 years ago and at this point I don't believe any of the standard Corvette parts companies (Eckler, Corvette Central, Paragon) has any remaining in inventory. In addition, the last version of the switch that GM sold came with H keys, so not correct for 71,72,74,75,or 76. And it's possible the last version GM sold also had a universal keyway, which means it wouldn't pass muster for 73 or 77 if a judge checked to see if the switch also accepted the E keyway ignition key during judging. In short, these alarm switches are getting rather hard to find and, therefore, rather expensive. In my search today, I found these:

Used, without key $100
Used, with D keys $180
NOS K keyway $220
NOS B keyway $280
NOS universal keyway $250

Even the "bargain" one for $100 would be gamble not knowing what keyway it has.

I don't want to put a damper on your attempt to take yours apart, but in my experience Michael's statement that he would "not call it easy", is an understatement in the hands of many of us, myself included. If you do undertake the challenge, could you post photos of how it turns out? I've love it if someone developed an approach for restoring those switches that's not as brute force as the technique I tried.

Gary

[Phil D.]

Re: Testing 1972 Alarm System

Phil,

It's not unreasonable that these alarm switches are no longer inexpensive or easy to find. According to my records, these were GM-discontinued more than 7 years ago and at this point I don't believe any of the standard Corvette parts companies (Eckler, Corvette Central, Paragon) has any remaining in inventory. In addition, the last version of the switch that GM sold came with H keys, so not correct for 71,72,74,75,or 76. And it's possible the last version GM sold also had a universal keyway, which means it wouldn't pass muster for 73 or 77 if a judge checked to see if the switch also accepted the E keyway ignition key during judging. In short, these alarm switches are getting rather hard to find and, therefore, rather expensive. In my search today, I found these:

Used, without key $100
Used, with D keys $180
NOS K keyway $220
NOS B keyway $280
NOS universal keyway $250

Even the "bargain" one for $100 would be gamble not knowing what keyway it has.

I don't want to put a damper on your attempt to take yours apart, but in my experience Michael's statement that he would "not call it easy", is an understatement in the hands of many of us, myself included. If you do undertake the challenge, could you post photos of how it turns out? I've love it if someone developed an approach for restoring those switches that's not as brute force as the technique I tried.

Gary

Luckily, it appears we won't have to disassemble the switch after all. We now have a functional alarm system. The chemistry experiment trick worked, but of course it still has to work when it comes time for the judges which is most likely next fall. Thanks for posting your research.