I just got a friend's old Monte Carlo, which at the time of arrival:

* interior lights would never turn on
* multiple false alerts in the message center
* brakes didn't work
* A/C and heat is either full blast (at 5) or nothing (1-4).
* Heated seat for driver's side not functional
* turn signal worked intermittently
* the gas gauge didn't work.

I replaced the hazard light once, and got the turn signal working consistently but not blinking. I replaced it again, and got the turn signal consistently working.

I replaced the key-switch in a attempt to fix the false alerts in the message center and the A/C, along with trying to find and repair faulty connections.

Now it:

* seems to have trouble sensing whether the doors are open or shut. The interior lights work perfectly when the security light is constantly on, and will not turn off when driving if the security light is off.
* A/C still an issue
* heated seat not functional (working on this last, most likely)
* When I brake slightly, and then turn sharply, the parking brake light will turn on. The parking brake was definitely not on. Sometimes it will turn on, on its own.
* It, every now and then, will refuse utterly and completely to start. (It wouldn't start after the new key switch was put in, and then the next time would, and tonight, would not.) Both starting relays were working fine. There was a main harness by the battery that when messed with, would cause the starting relays to click louder.

Any ideas for trouble-shooting, or in general?

(Whenever I have searched any of the issues this is having, or how to get a part out, this site has the answers, and I figured I'd just be more direct so I could thank you guys.)

 

Gremlins!

Unfortunately, I'm just getting started learning myself so I'm no help, but I had to comment. I recently got an '01 MC LS, but I didn't have any of those issues. (Except A/C which is just the compressor). I'm reaching here, but Haynes manuals have all the wiring diagrams in the back and they helped me get an understanding of how it all comes together. I bet if you start at ... say.. the Fan (a/c - heat) controls and work your way out from there you'll come across some rats nest that is the main root of your problem. or at least figure out what is and is not related.

Not much help, I know, but I wish you luck!

 

Lots of weird electrical problems that you can't figure out usually = BCM going bad.

Usually there is a blower motor resistor that goes bad and forces the fan speeds to only work on 1 setting, or just the high or low settings.

With the Security light on, the car will sometimes fail to start, that is the passlock system messing up on you. Could be related to the BCM, could be the passlock system itself.

Did you check your brake fluid? It might be slushing around and throwing the light because it is low.

 

Welcome to the site and good luck getting your car all figured out. This may help with the seat https://montecarloforum.com/forum/si...-jimbo7-25224/

 

Quote: "BCM going bad."

Well, the thing is, a lot of those random electrical issues got fixed after we changed out the key switch. Which is a good thing, as it is just about impossible to find osmeone who knows what a BCM IS much less is willing to repair one... plus that is a very expensive part.

And yes, I did check the brake fluid, as at the time it first gave this warning, it was working just about perfectly on the message system (now only gives off security and two things I know are broken and are too expensive and unimportant to fix), and it was low. The light still goes on when the same thing happens.

 

What part did you replace for the key switch?

If you still have the security problem, I would take a look and do some searching for "PassLock"

The brake light, perhaps there's a wire going bad?

 

The actual switch got replaced, but I'm familiar with the passlock part that you're mentioning as I came across it when looking at instructions for replacing the switch.

I imagine the wire has gone bad. Another thing that improved the problems was a cleaning solution in a lot of wires... if I could work out what wires were controlling that part, I'd be grateful.

 

Alright, now the ignition switch is being continually activated, the Back up LP Relay is clicking as we try to tear apart the dash to get into it to replace the switch, and it is sending a pulse through the speakers. The radio also reads 'cal err'.

 

Though the clicking could very well be one of the parts attached to the LP Back Up.