72 Anti-Theft Question

[Guy B.]

After a full restoration, can't seem to get the anti-theft alarm to function. All the wiring and door/hood switches (SX) are new GM. The horn was sent out and professionally rebuilt I bench tested it and it works perfect... nice and annoyingly loud. I went as far yesterday as to remove the key switch and when I touch the two terminals together I get a clicking from the relay in the rear jack storage tray so there is contact there I guess. I'm stumped. Anyone have any idea? Thanks!

[Harmon C.]

Re: 72 Anti-Theft Question

Do the switches at the back of the door have two or three wires connected to them?

[Guy B.]

Re: 72 Anti-Theft Question

Do the switches at the back of the door have two or three wires connected to them?

My guess is its a 2 like this picture, I would have to pull it out to double check. But they do look correct and have the SX marking. What are you thinking?

[Harmon C.]

Re: 72 Anti-Theft Question

If the switches have two wires the third is a ground to the metal plate the switch screws into. It is common for the wire to be broken off at the plate. It can be checked through the #3 body mount in the rear wheel well. If you have three wire switches the ground is in one of the wires.

[Mark E.]

Re: 72 Anti-Theft Question

Guy,

You need to diagnose the circuit, and pinpoint the problem. First step is to understand the circuit by studying the wiring diagram in the service manual. The alarm is a simple circuit and its components are readily accessible.

Likely failure points are components (door switches, relay, key switch, horn), connections and grounds. So with the alarm energized, systematically check for good ground and proper voltage at these points to locate the problem. Door switches are especially finicky on these cars and deserve special attention for proper operation.

A less likely failure is an open or shorted wire, which you can isolate by back probing.

[Edward J.]

Re: 72 Anti-Theft Question

Gary, remove one of the switch's and set alarm and just connect the two wires together to see of the alarm sounds. if not remove the relay in rear compartment and you can remove the tin cover(there are some tangs that you just straighten out) and maybe the points need cleaning, a piece of fine sand paper will work, they may just be glazed over from lack of use.

[Guy B.]

Re: 72 Anti-Theft Question

Gary, remove one of the switch's and set alarm and just connect the two wires together to see of the alarm sounds. if not remove the relay in rear compartment and you can remove the tin cover(there are some tangs that you just straighten out) and maybe the points need cleaning, a piece of fine sand paper will work, they may just be glazed over from lack of use.

Ed,

Yesterday I did removed the alarm key switch,and did just that.
I connected the two wire together got nothing but clicking from the relay in the storage compartment. The relay has not been used in a long while as that was original. I will try that.

[Terry M.]

Re: 72 Anti-Theft Question

Ed,

Yesterday I did removed the alarm key switch,and did just that.
I connected the two wire together got nothing but clicking from the relay in the storage compartment. The relay has not been used in a long while as that was original. I will try that.

Guy,
I think Ed was referring to the door switches, but maybe I misunderstood him.

All the rear keyed switch does is provide 12v to the relay when the switch is "on". If you don't get the same click from the relay when the key is turned, something is wrong with that switch. You can check the keyed switch with an ohm meter. If you don't have a volt/ohm meter troubleshooting this issue will be extremely difficult for you.

You may have multiple issues.

[Guy B.]

Re: 72 Anti-Theft Question

Guy,
I think Ed was referring to the door switches, but maybe I misunderstood him.

All the rear keyed switch does is provide 12v to the relay when the switch is "on". If you don't get the same click from the relay when the key is turned, something is wrong with that switch. You can check the keyed switch with an ohm meter. If you don't have a volt/ohm meter troubleshooting this issue will be extremely difficult for you.

You may have multiple issues.

Terry, I was getting the same clicking when the key switch was in and I turned it as well as when I removed it and touched the two contacts together. Either way I heard clicking. The key switch is also NOS GM that seems fine.

[Jeffrey S.]

Re: 72 Anti-Theft Question

Guy,
Did you check the flasher that sits next to the relay? If the flasher is bad nothing will get to the horn. I'm not sure which flasher was used in '72, but, for testing purposes, you can use any heavy duty flasher. By the way- DON"T leave 12 volts on the horn for a long period. It will burn out the coil. The horn was designed for intermittent honking only.
Jeff

[Guy B.]

Re: 72 Anti-Theft Question

Guy,
Did you check the flasher that sits next to the relay? If the flasher is bad nothing will get to the horn. I'm not sure which flasher was used in '72, but, for testing purposes, you can use any heavy duty flasher. By the way- DON"T leave 12 volts on the horn for a long period. It will burn out the coil. The horn was designed for intermittent honking only.
Jeff

Jeff what is strange is right now I have TWO electrical issues with this car, one being the alarm horn and the 2nd being the hazards. They dont work either. The directional's work perfect, the hazzrds no. I ordered a new flasher, that is the same as the one in the storage compartment. Wonder if the issues are tied together???

[Jeffrey S.]

Re: 72 Anti-Theft Question

Jeff what is strange is right now I have TWO electrical issues with this car, one being the alarm horn and the 2nd being the hazards. They dont work either. The directional's work perfect, the hazzrds no. I ordered a new flasher, that is the same as the one in the storage compartment. Wonder if the issues are tied together???

Guy,
Electrical has never been my strong suite but... I don't think they are tied together. I am pretty sure that they use the same number flasher (my '69 does). If it were me I would go to any parts store and get a new one for a few dollars and plug it in. Recently I was trouble shooting my system and at one point I got the same issue (I may have fried the flasher that was there) and replaced it. System now works perfect.
Jeff

[Guy B.]

Re: 72 Anti-Theft Question

Guy,
Electrical has never been my strong suite but... I don't think they are tied together. I am pretty sure that they use the same number flasher (my '69 does). If it were me I would go to any parts store and get a new one for a few dollars and plug it in. Recently I was trouble shooting my system and at one point I got the same issue (I may have fried the flasher that was there) and replaced it. System now works perfect.
Jeff

Jeff, this is what is back there now, as I did not do the restoration I don't know if it's new or not but going to replace

[Jeffrey S.]

Re: 72 Anti-Theft Question

Guy,
That's the one. The 4 way should be the same one. This may not be the culprit but it was worth a shot.
Jeff

[Guy B.]

Re: 72 Anti-Theft Question

Guy,
That's the one. The 4 way should be the same one. This may not be the culprit but it was worth a shot.
Jeff

Jeff, going to replace BOTH the one in the storage bin and the one in the fuse block. Then re-check alarm and hazzards. Would be ironic to have 6 figures into a restoration and get hosed by a 5 dollar flasher! LOL