The electrical systems on most '82 models are extremely simple compared to the ridiculously over-complicated cars we have today. If an electrical specialist is qualified to diagnose late-model cars, yours should be child's play. The exception though is Cadillacs. Those were the ones where GM put stuff to be tested by the owners. A lot of independent mechanics, and even GM mechanics, never got the training on systems that weren't used on many cars, so they didn't want to work on them.
Twice you said, "Firstly its the A/C. That turns on by itself and then would not be switched off." I don't understand what you mean. Are you saying the system turns on by itself, then you can't turn it off? Or are you saying for some reason you don't WANT to turn it off? If you have an early version of an electronically-controlled heater / AC system, that's going to involve a computer module that gave GM a lot of trouble. You can try unplugging it and plugging it back in a few times. If a light film of corrosion developed on the connector contacts, doing that will scratch some clean spots to make a better contact. They also had a lot of trouble with intermittent solder connections inside. You might be able to have the module checked for that at a tv repair shop if you can still find one.
The engineers at GM also put in a lot of troublesome automatic stuff for people who didn't know how to turn things on for themselves. Automatic headlights and automatically-dimming headlights were two of those "features". Anything that works by itself has to include some type of module or computer, and that's where the trouble starts. If you had a problem that was there all the time, anyone could easily diagnose the cause by simply unplugging things. When problems are intermittent, like these are, there is no way to know if what you did solved it. If it acts up again, you know you didn't fix it yet. If it doesn't act up, you don't know if it's solved or not.
The other problem is it may be hard to find a specialty shop that still has parts to rebuild a 32 year old computer. I tried to get one repaired for an '88 model about five years ago, but the factory-authorized shop wouldn't touch them anymore because they didn't have the parts. No mechanic wants to diagnose what he THINKS is a defective computer, then tell you he can't find a replacement to verify his diagnosis. We have to charge for our time, but we know you won't like getting a bill when we can't fix the problem.
I think where I would start is by asking around at some old car shows to see if you can find an older former Cadillac mechanic who remembers your electrical system. He may know of some common fixes or places to find replacement modules. For the heater/ AC module or controller, try flexing and twisting it or tapping on it while it's still plugged in and working. If anything changes unexpectedly, suspect broken solder connections inside it.
You might also consider a problem with a temperature sensor. Some cars had automatic temperature control for owners who didn't know if they were too hot or too cold, and needed the car to decide that for them. A defective sensor or a problem with the wiring for it could falsely tell the computer that AC is needed, so the system might turn on and you won't be able to over-ride it.
I don't have a good answer for the hazard lights. To the best of my knowledge, there was no computer involved with them. If they start flashing, treat them the same as on any other car. Look for the wiring harness running up the steering column and check for overheated or melted terminals in connectors, broken or frayed wires, particularly where they flex with the tilt-wheel, and overheated terminals on the signal switch. It would be helpful to know if it's the signal lights or the tail / running lights that are turning on.
Friday, December 12th, 2014 AT 11:09 AM