C3 Factory Anti-Theft Alarm

[Kevin Morris]

My 72's factory anti-theft alarm does not appear to be working. For one thing, when I insert the oval key into the lock on the back of the car, I can only manage to turn it about 1/8 of a turn to the right, none to the left. Perhaps this is correct, but it did not seem right to me. I have never been able to then open the doors or hood and get the horn to sound. Any ideas?

Kevin #39927

[Warren F.]

Re: C3 Factory Anti-Theft Alarm

Kevin: The lock cylinder should turn farther than that, more like a quarter of a turn, at least that is the way the '70 & '71's work.

[Larry Gawron]

Re: C3 Factory Anti-Theft Alarm

Kevin,
My '76 has the key switch on the front fender. The key turns about 1/4 turn to the right. In the past 27 years my alarm has stopped working twice. Both times it was the horn that stops working. It's hard to get to, above the left muffler. I have removed it, unscrewed the adjustment screw, sprayed WD40 down into the horn via the adjustment screw hole and down the megaphone. Replace the adjusting screw and adjust for the best sound. That's it! Again, the worst part it removing and reinstalling it.

[Jim T.]

Re: C3 Factory Anti-Theft Alarm

Kevin based on your initial problem of not being able to turn the key enough to properly activate the factory alarm system you could remove the switch very easily and take it to a local locksmith. You could also after removing it use a lock lubricant or WD-40 applied to the lock with the key entry end up for soaking and see what happens. The alarm switch is easily removed. Look from under the car and locate the backside of the switch and you will see that there is only a spring clip that retains the switch in the body. The two wires are easily removed going to the switch. Now to test the system after removing the switch just connect the two wires. First test is to verify that you have 12 volts in the power source wire that would activate the rest of the system when the switch is used, this will get you started. Looked at your 72's pictures. You have purchased a really nice 72 Corvette, enjoy it. With all this fixing of the small things you will be ready for the judging field.

[Harmon C.]

Re: C3 Factory Anti-Theft Alarm

Kevin If the screws are rusty that hold the wires on be carefull not to break them off the switch. Lyle

[Michael M.]

Re: C3 Factory Anti-Theft Alarm

I also have a '72, and just fixed my alarm also. I used a test light to trace the fault to the switch. I removed the switch, cleaned it, and replaced it. That corrected the problem. The above suggestion is a good one ... I don't think I needed to even take the switch off. I probably could have cleaned itin place ... my switch was rusty, and I ended up breaking one of the little screws ... no big deal, but it would have been just as easy to have broken one of the terminals - which would have been a BIG deal.

If it turns out to be the switch, which it probably will - Try to clean it in place first.

[Gary S.]

Re: C3 Factory Anti-Theft Alarm

My 72's alarm also didn't work when I bought it. A quick removal of the switch, cleaning with electrical contact cleaner, followed by a shot of WD-40 helped. Then I cleaned the two contacts just to be sure. Works well.
Gary

[Shawn Woodend]

Re: C3 Factory Anti-Theft Alarm

My 73's alarm horn has a white powdery crust on it not surprising it does not work. Any thoughts?

[Roger S.]

Re: C3 Factory Anti-Theft Alarm

Put a jumper wire across the terminals on the switch and then see if the system works. It's a quick test to see if there are other "issues" that need to be addressed. If you want the jumper can be fused to eliminate a short in the circuit causing other problems.
I have a system checkout write-up that I can email if you want it.

Roger

[Michael W.]

Re: C3 Factory Anti-Theft Alarm

'73s did not come from the factory with white powdery crust. This sounds like a dealer installed option called 'corrosion'

Sounds like your horn has bit the biscuit.

[Kevin Morris]

Re: C3 Factory Anti-Theft Alarm

Roger,

I would like to see that writeup, please email it to me...and Thx. I took the switch out last night, as well as the horn. I clean all the electrical contacts on both. The switch DID turn about 1/4 of a turn afterall. I had one of the wires very loose of the switch, so I soldered it. I then tested the horn, by taking the connections off of my car's regular horns and hooking one of the connections to the alarm horn. Not knowing whether this was an adequate way of testing the alarm horn...the horn did not work. I re-installed switch, horn, etc. and tried to arm the alarm with doors shut. When doors were then opened...NOTHING! With one of the doors open, I then tried arming the alarm, and I could hear a clicking noise (I believe it was coming from the alarm switch located in the passenger-side storage compartment), but the horn still did not sound. Sounds to me like my horn is bad??

Kevin #39927