72 Alarm System

[Larry M.]

The alarm horn on our 1972 sounds when wired directly to a 12-volt source, although not at any other time, such as when the alarm switch is activated and a door opened; I don't see any power going to the alarm flasher; the alarm relay clicks once when connecting the three-wire connector to it, but then makes no further sounds.

From that bit of work, it seems to me like the relay is bad. If that's the case, is there anything that can be done to the relay to make it work? Am I correct that the relay should send constant power to the flasher all the time (when switch 'on' and door open), and the flasher should then 'flash' the sounding of the horn?

Thanks!

Larry

[Terry M.]

Re: 72 Alarm System

12v goes through the alarm switch (if the alarm switch is ON) to the relay. The ground to actuate the relay comes from the door or hood switches. The flasher makes the horn go off and on (flash).

Check for 12v at The relay with a meter. Use a ground jumper wire to ground The relay -- No I don't know what color is ground. Some of the factory service manuals have a schematic for the alarm system. I think 1972 was the first to have it.

[Larry M.]

Re: 72 Alarm System

Terry,

Thanks for your info; yes, I have the service manual, and it does have a separate wiring diagram for the theft alarm (black=ground, pink=12v, white goes to flasher).

I'll ground it as you suggest, and check for 12 volts.

Do you know of any 'repair work' to attempt on the relay, if that is the failed item?

Larry

[Terry M.]

Re: 72 Alarm System

I have no experience repairing the relay, and other than cleaning the contacts I don't know what you could do to fix it. I don't suppose you have considered looking for another relay.

In my experience the primary failure item is the pin switches that provide the ground. Next is the horn itself. Both usually give way to corrosion.

[Bill C.]

Re: 72 Alarm System

hey--

if you get in dire straits

I have an extra NOS one for the car.

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also -
I remember reading about someone who can rebuild relays, maybe I saw it in Hemmings.

[Jim T.]

Re: 72 Alarm System

Doug Fry made an earlier post that he found the relay at Paragon for his LT-1's alarm system.

[Larry M.]

Re: 72 Alarm System

Bill and Jim,

Thanks for the info, guys. I suppose that I'm still at the point where I'm trying to determine if in fact the relay is bad before I replace it with either a NOS or a repro.

From what I've written, does it sound like a bad relay to you?

Thanks!

Larry

[Jim T.]

Re: 72 Alarm System

Lawrence I don't have an C3 factory alarm in my 68 or 70. I do have a complete wiring harness for the the factory alarm I have had for 35 years that I got from the dealer when I bought my 70 new, just have not installed it yet. Might try contacting the Doug Fry the owner of the LT-1 that posted before you ,not a lot of posts, and see if he was experiencing the same problems with his alarm system.

[Jack H.]

Re: 72 Alarm System

So, pull and bench test the relay... It's no different than any other horn relay. Depending on design, the relay gets B+ power and ground then connects to its input/output.

On Delco Remy horn relays, the top cover is embossed 'S' and 'H' to designate the functions of the bottom side slide terminals directly below. 'H' means horn and that's the output power side that feeds the horn terminal.

'S' means switch and that connects to the steering column's horn switch that makes contact to ground closure to fire the relay. Instead of connecting the horn relay on the bench to an actual horn, use another load like an ordinary light bulb.

You ought to make the test load (light bulb) turn ON/OFF each time you ground the 'S' terminal on the relay. There's no reason to guess as to whether the relay is functional or not, just bench test it.

[Larry M.]

Re: 72 Alarm System

Jack,

Thanks for your test method; I will do that to determine my next step.

Larry

[Kenneth T.]

Re: 72 Alarm System

Anyone ever rebuild the horn? I put power right to it, good ground, and no blow, it's a '71. I have not been able to locate anyone who sells repos or rebuilts so the only way is to try to fix this one. Zip sells a kit , but it requires popping the rivits and taking apart the diaphram chamber. I have never done one....yet.

[Larry M.]

Re: 72 Alarm System

Jack,

Thanks, I tested the relay per your instructions, and my test light lit.

I then tested the horn flasher. I hadn't considered that initially, because it was relatively new. Although it is relatively new, it turns out that it is absolutely inoperative; I swapped it with my known-to-be-good directional flasher, and my directionals no longer flash.

I'm off to pick up a flasher.

Simple fix, thanks for your help.

Larry

[Jack H.]

Re: 72 Alarm System

Ain't the scientific approach wonderful? Saves a lot of time and parts purchased for substitution/testing...