at 3am my 92 vettes car alarm started going off. Went outside turned it off started the car fired right up lock the doors went back inside two minutes later it's going off again. Disconnected the positive battery terminal.

it snowed yesterday and there where no fresh footprints around it.

What could be going on with the car to cause this?

Check for bad door or hatch "open/closed" switches

Most false alarms come from the shock sensor usually mounted under the dash or side kick panel if you can find it try and adjust it or unplug it. should be a small black or clear box with a red led light in it,if a door or hatch is open you should here a diiferant amount of chirps when you arm it than usual.

Arm it? I do not have a key fob if that is how you arm it. I just use the power lock switch on the door when I park.

Hmmm must just be the factory alarm don't think those have a shock sensor.

OK would the switch that you speak of be the same switch for the door open cabin lights?

I believe you arm it from the door lock button or by locking with the key,but you can only disarm it with the key.

correct it is armed by the power lock switch or key and disarmed by the key only. but after i disarm it and lock the car again the alarm will go off again.

Is there a way to completely get rid of the anti theft till i can find the problem? pulling the fuse i will lose the horn as well

yes

Ok got an idea. I got to thinking about when the alarm is going off. it seams to be at night when the temperatures drop. Is there a seal that might need to be replaced? A seal that when it gets cold will shrink and pull a switch away from the door or hatch?

One of the door switches might be sticking slightly.

Try spraying both door switches with some WD-40.

Yes, instead of locking the door via the PDL switch move the lever under the door handle manually then close the door and it will not arm the factory alarm.

When it goes off it sounds only the horn and not an additional siren right?

If your 86 is like mine there are 2 pin switches in each door. One is by the hatch release at the ends of the door and the other is in the doorjamb by the dash. I'm thinking the alarm uses the one in the doorjamb. A simple test would be (get a helper unless you have 3 arms) to depress both switches with the door open, press lock on the PDL and see which one triggers the alarm when released. Have the door key ready in the lock so as to quickly shut it off when it sounds. Once verified the "trigger" switch that would be the switches I'd check first both on driver and passenger doors.

Actually, lubrication should be done with oil or grease, not WD40. WD40 is great for some things, but it is basically a coating of silicone (or some such). It works great for a short while, until the coating wears off, then things are worse than ever. (WD stands for Water Displacement. It actually removes moisture (including oil) from whatever it is sprayed on).

It's possible the weatherstripping could shrink a little but I don't know if that could make the switch go off. Check that the switches all work and that the adjustment looks right, don't want the interior lights to come on if the door (or hatch) are just slightly loose.

Locking the doors with the manual door locks (not the key) should not arm the alarm.

Ok here is what i have done hopefully it works.
upon closer inspection the drivers door switch was loose. pulled the door panel off to find that it was no longer screwed into the mount behind the door. 2 new machine screws and double nutted each of them. the switch itself wouldn't turn off the radio after opening the door with out giving it a little wiggle by hand. sprayed it with a little WD-40 and worked it around a little. WORKING PERFECT NOW!! Was going to replace the switch since i had everything apart anyway but no one in town had one so if it starts acting up again I will do the WD-40 again (as i know WD-40 is only a temporary fix) and order a new switch.

A huge THANK YOU for everyone who replied and gave advice or their two cents!
Daniel

with the window down test locking door with the key did not set off any alarm thanks good to know info for the future