Theft Alarm Problem for Early 72 Coupe

[Norm C.]

The theft alarm has stopped working. Any door or hood open will not trip the alarm. I started at the rear key switch and it doesn't appear that I have power incoming to the switch. The wiring diagram shows the power switch is supplied with a connection, but doesn't offer as to where that connection is found. All fuses work. Questions are:
1. Where does the power for the alarm system originate from?
2. Is the alarm system fused, if so, which fuse is used?
3. Any help or suggestions on how to track the power sourcing through
the system?

I feel if I can ascertain that the system is getting power, I could track down any door or hood switch failures..........

Thanks to all in advance for sharing your knowledge/experience!!!

[Roger S.]

Re: Theft Alarm Problem for Early 72 Coupe

Send me an email and I will attach my schematic and troubleshooting checklist for a 73. It should be similiar to your 72.

Roger

[Chuck B.]

Re: Theft Alarm Problem for Early 72 Coupe

Check to ensure that the alarm horn is grounded.

[Harmon C.]

Re: Theft Alarm Problem for Early 72 Coupe

While checking the ground at the horn bench test the horn. When no switch will sound the alarm most of the time the horn has a problem.

[Gary S.]

Re: Theft Alarm Problem for Early 72 Coupe

You can pull that horn out fairly easily. Only a few slices in the wrist from the gas tank. You can bench test it by placing it in a vice and using your 12v battery charger set on the low setting, often 1 or 2 amps. That is how I did it when I was checking out why the one on my 72 didn't work.

If you need specific photos of any of the components for a 72, let me know.
Gary

[Jack H.]

Re: Theft Alarm Problem for Early 72 Coupe

1. Where does the power for the alarm system originate from?

Originates from the fuse block and runs to the rear of the car on the rear wiring harness (one version for standard car and another for UA6 optioned cars). Note: interconnect to the dash harness is via a plug-in connector located behind the LH interior kick panel.

2. Is the alarm system fused, if so, which fuse is used?

Yes, the circuit is fused and your copy of the owner's manual will identify the fuse as well as the Chassis Service Manual. Look for a 25A fuse that powers the cig lighter, clock, courtesy lamps, glove box lamp, Etc.

3. Any help or suggestions on how to track the power sourcing through the system?

Unfortunately, this option is NOT depicted in the standard car wiring diagram and the section of the AIM dealing with the UA6 does not provide a pictorial of the difference(s) associated with option. Don't you just LOVE Chevy's documentation!

That leaves you with having wire/color code/routing info on the base car. So, any 'extra' wires in your rear wiring harness can be attributed to the UA6 alarm option...

Tips: (1) look for badly oxidized contacts at the alarm switch, and (2) bent or loose mating connections in the rear harness to dash harness connector.

[Norm C.]

Re: Theft Alarm Problem for Early 72 Coupe

Thanks to Lyle, Gary, Jack & Chuck..... I'll ck out the horn,,,, I put a 12 volt current tester to each terminal of the key switch and neither terminal would lite. At the same time the courtesy/cig lighter work, (which I surmised would be the fuse for the alarm as well) and all work, so I'm thinking its not a fuse issue.

Additionally, I located the relay plug and flasher behind the psgr side storage with the jack. Question: There appears to be a grey and green wire terminated there, which I'm suspecting may have been the power source for rear window defogger, but I don't have that option. Also there is an orange & black wire that don't appear to be a part of either of the connectors in that area..... would those be for????????

Lastly, to Jack.... Referring to the connection your mentioned being behind the LH kick panel,,,,,, Is that the connecttioin for the Alarm harness to connect to the dash harness as its source of power from the fuse panel?

Thanks again guys...... this discussion board is so damn helpful because of guys like you willing to share your expertise & that "been there done that" kind of help!!!

[Michael G.]

Re: Theft Alarm Problem for Early 72 Coupe

Norm,
My 71 has the factory alarm and I found a bad connection on the horn relay (inner fenderwell of driver side. The blade connector of the frontmost wire was not properly attached and had poor contact. This along with bad contact of the flasher (rear compartment) were the culprits. This fix also revived the "key in ignition" warning buzzer. Nice bonus Mike