(help!!) Information On 1972 Vette Anti Theft Alarm System

[Bill E.]

Hi guys,
I m trying to get my alarm system to work. This is what i have. My two door anti theft switches are dissconnected right now and I m in the process of putting new switches in. The system didn't work, when I got the car. I took the three wires, on the driver door jam and tied them together, turned my key on to set the alarm and the horn makes a clicking sound (like a turn signal would make). I put a new turn signal flasher in next to the relay "Is there a special flasher?". When I disconnect the wires, it still makes the sound I mentioned above. When I turn the key off and back on again it doesn't do anything after the wires are dissconnected; which I think is working ok. I want to know why my horn will not blow and are the lights soppose to flash when the horn goes off (when the alarm is activated). Thank you
Bill E
70 - 72 vette

[Bill E.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Hi Guys. I Did Test The Horn And It Works . When I Was Testing The System The Horn Went Bad. So I Used The Horn For The Car And That Horn Went Bad To. I Do Not Know What Is Going On. The Horns Will Make A Turn Signal Sound But Will Not Blow. I Jump The Horns To A Battery And They Will Only Hum Now. So They Are Bad Now.

[Terry M.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

The 1972 (1968-197X? option alarm UA9 for 1969-1971 and standard after that) -- operates only a horn that is mounted to the rear bulkhead above the driver's side muffler. It is not uncommon for this horn to fail -- rust internally, and corrosion at the electrical connection are the killers, and I would bet that is what has happened in your case based on the sound you describe.

FYI:
The system operates on 12-volts that goes to the key in the rear panel. With the key on that 12-volts goes to the relay in the jack storage compartment.

The door switches (at the hinge pillar) make a ground connection when the door is opened (either side). That ground goes to the other side of the coil of the relay in the jack storage compartment. Sometimes those door switches corrode enough that they don't make good connection to ground. They can be cleaned sometimes by simply rotating the pin and sometimes they need to be taken out and cleaned with abrasive paper.

I can't describe the rest of the circuit from memory, nor can I tell you for sure what reference has the diagram.

The flasher is the same unit used for the hazard flashers, but I can't remember the number on it. The relay is a little hard to come by, but I have seen NOS ones available from time to time, and if you don't intend to have your car judged I am sure there is a substitute available at Radio Shack.

Work on the horn first. If there was a clicking sound, I think your circuitry is good. You just need to make the horn work.

You should also consider building a library of reference materials to take care of your baby. The Factory Service Manuals (there are two for 1972 -- Service and Overhaul) an Assembly Instruction Manual are the start. Both are available from the "NCRS Store" on the radio buttons at the top of the page. If you intend to work on your Corvette these are the starter books and your library will build from there.

[Terry M.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Be sure you are using large enough wires for the + and - connections. Horns draw a lot of current and you need thick wires and good connections to make them work. On the other hand they may be rusted internally and you may have just heard the last of them. You can rebuild them -- if you are handy, or there are folks who advertise this service in The Driveline.

[Bill E.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Hi Terry I Drop Down The Horn First. Then I Tested The Horn To A Battery Horn Work Find.then I Hook The Orig. Wire Connection To The Horn And The Ground Wire Where The Bolt Is That Mounts To The Body.i Connected The Orig Wire And Put A Nut And Bolt To The Ground Wire And Left The Horn Hang.i Have Both Door Switches Un Hook. I Took The Driver Side Wires (three Wires And Hook Them All Together.i Turn The Switch On With The Key And The Horn Only Made A Turn Signal Sound .i Disconnected The Three Wires At The Door And Turn The Key Off And Turn On To Reset And The Horn Stops Making The Turn Signal Sound.so I Took The Horn Down And Retested It To A Battery And I Used Heavy Wire And Now The Horn Is Not Working Right Any More.i Try My Horn On The Car To Try The System Out And That Horn Work Befor I Try This And The Same Happen To That Horn. Now I Have To Bad Horns. P.s Out There I Am Going To Spring Carlisle In Two And Half Weeks My Spot Is J 25 Corvette Row Ask For Bill Iam Looking For Two Horns One For Engine Comp. And One For The Aanti Theft Alarm Mounts Over The Rear Driver Muffer. I Am Looking For Two Good Used Ones .thanks Bill

[Jim T.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Bill, do you know that one of the three wires to the door pillar switch is for the door ajar indicator lamp?

[Harmon C.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

The three little wire ends push back inside the round plastic holder and are easy to break. One wire is the ground one the alarm horn and the last the alarm light. To others who read this post in Dec. of 72 GM went to a two post switch at this location and a wire was welded to the plate the switch scews into and run to a common ground. Many times the wrong switches are used.

[Jeffrey S.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Lyle:
I just took both door ajar switches off my '69 and found that if, after the switch is removed from the jam, you compress the center post exposing the top of the connector and gently slide a pin into the plastic toward the outside of the recepticle, the tang compresses and the terminal comes right out of the plastic. Anything larger than a pin could break the plastic. Just my experience.
Jeff

[William N.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

One of my experiences was to find after trying a couple of horns, that the terminal in the connector to the horn was corroded. Since it is exposed to the environment (and Humidity) being externally mounted, and lets face it rarely used, the terminal had developed corrosion on it that wasn't apparent till I backed the terminal out of the wire. I cleaned the terminal, and the horn worked fine.
Unfortunately that doen't expalin how a horn wouldn't work after tested back on the bench, but it might be something you haven't tried. and it did fix it so I passed my PV.

[Bill E.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Hi Guys. Thanks For The Help.i Have To Buy Another Horn To Try The Alarm System . I Put In A New Flasher Next To The Rlay.i Put In New Door Ajar Switches.when I Turn The Ignition Switch On And Open The Door The Door Ajar Lights Up In The Dash (works On Both Doors).if I Have A Bad Alarm Relay Whats Happens When It Does Not Work.because I Check The Switches Wires And They All Look Good.any More Ideas Out There Thanks. Bill

[Harmon C.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Lyle:
I just took both door ajar switches off my '69 and found that if, after the switch is removed from the jam, you compress the center post exposing the top of the connector and gently slide a pin into the plastic toward the outside of the recepticle, the tang compresses and the terminal comes right out of the plastic. Anything larger than a pin could break the plastic. Just my experience.
Jeff

Jeff when you insert the ends back into the switch if the tang does not hold in the plastic housing to complete the circut the alarm will not sound. Many times this is the cause of alarm failure after the horn is repaired and the ground cleaned up. Those little brass ends slide down inside the white plastic too deep and no contact is made.

[Jeffrey S.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Lyle:
You are absolutely correct that the tangs have to set properly in the plastic holder. What I do on any terminal when replacing it, is to spread the tang away from the terminal so that when it is inserted it can spring out to catch the "step" in the receptical. Although these are very small terminals the same procedure applies. If they are corroded or very weak they can be replaced-Paragon carries them , made bt Lectric Limited.
Jeff

[Terry M.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Jim,
Are you sure the door ajar switch (at the back of the door jamb) connects to the alarm? On my 1970 the alarm switch is the same switch that lights the courtesy lights -- at the front of the door jamb.

I do have a vague recollection that once the alarm system became standard (1972) they moved the location of the switch -- so you may be on the right one -- I just am not sure.

You must have had the right wires connected at one time if you heard a turn-signal like clicking from the horn. That just indicated that the horn bit the big one.

I am pretty sure that any horn will work electrically just to test the system. It is the mounting bracket and straight trumpet that makes the alarm horn unique. If all you want to do is test the system, go to your FLAPS and buy the least expensive horn they have.

[Terry M.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

For what it is worth the Vette Vues Magazine (May 2009) that just arrived has a diagram of the UA6 alarm system (dated 1969) on page 118. There is also a diagram in one of the Factory Service Manuals -- 1972 I think.

[Vincent F.]

Re: (help!!) Information On 1972 Vette Anti Theft Alarm System

Is there any way to rebuild the horn, I just tested mine direct to a battery and got nothing, looks rusty inside. Its rivited together so I dont see how.