'79 Alarm Problem
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
'79 Alarm Problem
As part of refurbishing the door mechanisms I replaced the alarm key switch as its leads had been yanked out. I also replaced the non-working alarm horn. Despite the replacements, the system was non-functional until recently.
Now, on rare occasion, I'll hear a very muted chirp or two from the alarm horn when I shut off the engine. Then when I open the door to get out, the alarm sounds and I have to mess with the key lock to get it to shut off.
I installed a remote keyless entry system so I never lock or unlock the driver door with a key and don't understand how the system is arming.
Is that rather finicky looking arm/disarm switch one of the piece-of-crap import replacement parts that rarely--if ever--work properly?
Now, on rare occasion, I'll hear a very muted chirp or two from the alarm horn when I shut off the engine. Then when I open the door to get out, the alarm sounds and I have to mess with the key lock to get it to shut off.
I installed a remote keyless entry system so I never lock or unlock the driver door with a key and don't understand how the system is arming.
Is that rather finicky looking arm/disarm switch one of the piece-of-crap import replacement parts that rarely--if ever--work properly?
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
As part of refurbishing the door mechanisms I replaced the alarm key switch as its leads had been yanked out. I also replaced the non-working alarm horn. Despite the replacements, the system was non-functional until recently.
SO...I can only assume that the switch that you installed on the back of oyur lock cylinder was the CORRECT one....because they can be wrong,,,even though they look right. This switch has to be installed CORRECTLY in order for it to arm/disarm the system.
Now, on rare occasion, I'll hear a very muted chirp or two from the alarm horn when I shut off the engine. Then when I open the door to get out, the alarm sounds and I have to mess with the key lock to get it to shut off.
YES...this is when you rally need to make sure the switch on the backside of the lock cylinder is PERFECT. When I repair these...I take my time to make sure the switch is good to go....and NOT so touching that the slightest movement of the lock cylinder it arms the system. AND this can also be attributed to a worn shaft on the lock cylinder itself or the pawl that attaches to it because the cycling of it being locked and unlocked is causing the switch to NOW be past where it NEEDS to be and ready to arm again....OR did not go far enough due to this wear.
I installed a remote keyless entry system so I never lock or unlock the driver door with a key and don't understand how the system is arming.
Using a remote to lock and unlock...and NOT KNOWING if you tapped into the wiring to arm and disarm the system..I can not comment on this.
Is that rather finicky looking arm/disarm switch one of the piece-of-crap import replacement parts that rarely--if ever--work properly?
SO...I can only assume that the switch that you installed on the back of oyur lock cylinder was the CORRECT one....because they can be wrong,,,even though they look right. This switch has to be installed CORRECTLY in order for it to arm/disarm the system.
Now, on rare occasion, I'll hear a very muted chirp or two from the alarm horn when I shut off the engine. Then when I open the door to get out, the alarm sounds and I have to mess with the key lock to get it to shut off.
YES...this is when you rally need to make sure the switch on the backside of the lock cylinder is PERFECT. When I repair these...I take my time to make sure the switch is good to go....and NOT so touching that the slightest movement of the lock cylinder it arms the system. AND this can also be attributed to a worn shaft on the lock cylinder itself or the pawl that attaches to it because the cycling of it being locked and unlocked is causing the switch to NOW be past where it NEEDS to be and ready to arm again....OR did not go far enough due to this wear.
I installed a remote keyless entry system so I never lock or unlock the driver door with a key and don't understand how the system is arming.
Using a remote to lock and unlock...and NOT KNOWING if you tapped into the wiring to arm and disarm the system..I can not comment on this.
Is that rather finicky looking arm/disarm switch one of the piece-of-crap import replacement parts that rarely--if ever--work properly?
DUB
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Thanks DUB! Looks like it's time for a trip back into the door to examine position and function of the key switch 
I'm 100% certain that the remote keyless entry system I installed has NOTHING to do with this as it has no connection whatsoever to anything in the alarm system. It connects only to the locks, the horn and the ignition via neutral safe circuit and new relay and functions perfectly.
I'm 100% certain that the remote keyless entry system I installed has NOTHING to do with this as it has no connection whatsoever to anything in the alarm system. It connects only to the locks, the horn and the ignition via neutral safe circuit and new relay and functions perfectly.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
I will need to look at my wiring diagram for your 1979 and just make sure that what I am thinking is correct.
I DO KNOW that when GM went to the alarm system withe the theft deterrent control module...the power door lock switch DID arm the system when you used them to lock the doors when leaving the car....but after the day I had today...my head is spinning and I do not think that your system does that....because you car is the early relay and flasher design.
DUB
I DO KNOW that when GM went to the alarm system withe the theft deterrent control module...the power door lock switch DID arm the system when you used them to lock the doors when leaving the car....but after the day I had today...my head is spinning and I do not think that your system does that....because you car is the early relay and flasher design.
DUB
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Thanks again DUB.
I've studied the schematics carefully as well as the owner's manual.
According to the manual the ONLY way to arm and disarm the system is via the driver door key. Neither the manual interior locks nor the power locks can arm/disarm. Such is obviously why that key switch is so finicky. I did some resistance tests of that switch both before and after installation but got erroneous results--it seemed to work properly at times but not at others. The original anti-tamper switch was fine.
Only after installation of the new key switch did I find that the alarm horn was bad. I found an original replacement for the horn and expected the system to work properly yet it was completely dead. The original alarm wasn't a priority for me so I just left it for another day...
...that other day came when the alarm began to sound for no reason...
I've studied the schematics carefully as well as the owner's manual.
According to the manual the ONLY way to arm and disarm the system is via the driver door key. Neither the manual interior locks nor the power locks can arm/disarm. Such is obviously why that key switch is so finicky. I did some resistance tests of that switch both before and after installation but got erroneous results--it seemed to work properly at times but not at others. The original anti-tamper switch was fine.
Only after installation of the new key switch did I find that the alarm horn was bad. I found an original replacement for the horn and expected the system to work properly yet it was completely dead. The original alarm wasn't a priority for me so I just left it for another day...
...that other day came when the alarm began to sound for no reason...
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
I will need to look at my wiring diagram for your 1979 and just make sure that what I am thinking is correct.
I DO KNOW that when GM went to the alarm system withe the theft deterrent control module...the power door lock switch DID arm the system when you used them to lock the doors when leaving the car....but after the day I had today...my head is spinning and I do not think that your system does that....because you car is the early relay and flasher design.
DUB
I DO KNOW that when GM went to the alarm system withe the theft deterrent control module...the power door lock switch DID arm the system when you used them to lock the doors when leaving the car....but after the day I had today...my head is spinning and I do not think that your system does that....because you car is the early relay and flasher design.
DUB
I haven't fully troubleshooted the system but presume that the switches are all working properly.
Le Mans Master
Joined: Dec 2003
Posts: 5,381
Likes: 416
From: N J
DUB helped me with this also when I was having this same problem on my 77. Thanks again.
I would lock the door from in the car, open the door and the alarm would sound. There is a VERY thin line between on and off in that switch, the contacts are very close and touchy.
On my 77 switch it has a yellow plastic insert that the cylinder shaft goes through and actually turns the contacts in the switch with the key. It had 2 nibs on it that line up with the contacts to grab and rotate them.
What I did on the bench was remove the yellow insert and with a tiny dremmel tool cut 2 new slots in the copper contacts so when the insert was replaced in these new slots there would be plenty of clearance and no chance of it going off accidentally, but also close enough to where the contact would arm and disarm with the key.
It may sound confusing but with the switch out and studying it you will see what I mean.
I would lock the door from in the car, open the door and the alarm would sound. There is a VERY thin line between on and off in that switch, the contacts are very close and touchy.
On my 77 switch it has a yellow plastic insert that the cylinder shaft goes through and actually turns the contacts in the switch with the key. It had 2 nibs on it that line up with the contacts to grab and rotate them.
What I did on the bench was remove the yellow insert and with a tiny dremmel tool cut 2 new slots in the copper contacts so when the insert was replaced in these new slots there would be plenty of clearance and no chance of it going off accidentally, but also close enough to where the contact would arm and disarm with the key.
It may sound confusing but with the switch out and studying it you will see what I mean.
Last edited by John 65; May 30, 2016 at 08:35 PM.
Pro
Joined: Nov 2014
Posts: 503
Likes: 66
From: Florida
Disconnect the factory alarm and put in a Viper Alarm. I did this on my 81, the cost was only 59 bucks, much cheaper and easier trying to buy original parts and track down all the issues. It will take you a weekend to install and you will have a much more robust system with the addition of a starter kill and separate alarm siren. If you have power locks it will also give you keyless entry.
Here is a write up and tips I posted previously if you are interested
https://www.corvetteforum.com/forums...981-vette.html
Reaper
Here is a write up and tips I posted previously if you are interested
https://www.corvetteforum.com/forums...981-vette.html
Reaper
Last edited by Reaper19; May 31, 2016 at 12:47 PM.
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Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
By the schematics there is no proper way for the power locks to arm the system when you exit because it would immediately trigger the alarm with the door open. ZERO electronics in the system to include a time-delayed arming relay.
I haven't fully troubleshooted the system but presume that the switches are all working properly.
I haven't fully troubleshooted the system but presume that the switches are all working properly.
I AGREE with 'John 65'. The special plastic piece that fits into the switch that goes onto the backside of your lock cylinder CAN BE really touchy....especially if it is a reproduction part.
DUB