Hi, I have a 1973 Corvette with the base 350 engine and 4 speed transmission. I have owned the car for 48 years and after 40 years of ignoring the anti-theft system, which had quit working, I decided to make it operational again. I have spent a few days troubleshooting and making corrections until I finally got the system working with the passenger door and hood. However, the driver's door is still unresolved. There are two wires, a white and a light blue, that attach to the anti-theft door sensor. When I bypass the blue one (which is the ground) by grounding the white wire directly to the battery negative terminal, it works as it should. I suspect that, wherever the blue wire is attached to ground, there is rust or some other issue. Would anyone know the location where the blue wire is grounded? It looks like it runs behind the carpet located behind the driver's seat, but I hate to start taking apart the interior when I'm not sure. Any help would be greatly appreciated.

 

Welcome to the forums. If you could find a service manual might help you. In the Haynes manual I have it shows the blue wire connects the two door contact switches together, then t-ing off and running to the dash cluster. The manual shows 3 wires on the door contacts Lt blue, wht, and blk. The blue wire is grounded from the door contacts.

 

Thanks for the reply, I do have a Helm's manual but I didn't catch the detail regarding the "T" of the blue wires. I believe that "T" is located under the carpet behind the seats and reinforces my thought of looking there next. My manual also shows the 3 wires at the door switch but that is not the case on my car (I have just a white and lt blue). There is a second switch in the door jamb that operates the courtesy lights, perhaps that switch has 3 wires. My diagram did not show 2 switches, however. Unless I find out differently, I am going to lift up the carpet and see what I find. Thanks for going through the trouble to look into this for me.

 

The manual I was looking at was also showing one switch with a wire for a seat pressure switch and seat belt buckle. that part of that circuit. There is the alarm relay in the console, not sure if that blue wire goes there for a junction, the manual doesn't show that. You might need to peek underthe carpet. The manual was showing the blue wire going to one switch then running across the car to the other side, the junction was at the switch. Not sure if that helps..

 

Thanks again for looking into this further for me. I was searching the web for more information regarding my problem and found a very old post that was very helpful. According to this person, During the 1973 model year the door switch design for the alarm was changed from a 3-wire switch to a 2-wire switch. The 3-wire switch-had a black, lt blue, and white wire. The black was the ground wire. After the switch to 2-wire, the black wire was attached to the switch mounting bracket and then grounded on the other end. This left just the lt blue and white wire connected to the switch (this is what I have). The white wire is the ground that activates the alarm relay and the lt blue wire operates the "door ajar" dash light. With that in mind, I went out this morning and removed the switch at the driver's door and touched the blue wire to the mounting bracket and the "door ajar" light came on as it should. I then touched the white wire to the mounting bracket with the alarm switch turned on and the alarm beeped as it should. At this point, I suspected the switch was bad even though my continuity check said it wasn't and moved the switch from the passenger door to the driver's door. The alarm worked again. Still being suspicious, I re-installed the original driver's side switch and the alarm worked great. At this point, the alarm system is working for the hood and both doors and I don't know why. I decided to pull the carpet behind the seats and inspect the wiring. Everything looked OK and I was able to locate the ground wire from each switch mounting bracket. I removed them from their grounding points, cleaned and re-attached. It was a bittersweet moment, I'm glad the system is now working and gained a lot of knowledge about it but did not gain the satisfaction of knowing what the problem was.


Ground wire in background. Driver's interior quarter panel trim removed.

Ground wire detached and cleaned. Note the blue and white wire coming inside from the alarm switch.

 

I'm glad you got it sorted out. It's really a simple system but with bad contacts and bad grounds it can be a pain. I had about the same issue a few years ago on the 77 the alarm didn't work, cleaned all the contacts and it finally started working. It also has a Clifford alarm system on it when I bought it. It also uses the same factory door and hood switches. It works with a siren,using the same ground door switchs to the interior lights use. I haven't set off both alarms at the same time yet, that has to be annoying.

 

It sounds like a nice system. I'm sure it would wake people up at night. I put grease on all my contacts after cleaning; I think it keeps them from oxidizing over time.

 

contact grease is good. I try and make it a habit when the doors are open to push the door switches in and let my finger slip off so it pops out to hammer the contacts. I worked on a 79 Corvette at one time that had an intermittent short in the interior lights on the orange wire. never found the issue after 2 hours of searching. Ended up installing a reset fuse and let it go. I always remember the issues I couldn't find.

 

Next up I am going to see if I can get the cigarette lighter working again. It seems simple, but I am not going to presume it will be after this.

 

Yes that is simple. Old lighters don't work as good as new ones. Time and moisture destroy them. Same with the Fuse block.