This just started about a week ago. When I start my car the Passcode light on my instrument panel flashes on and off. While parked it will click and cause my headlights to flash. When I put it in drive the headlights stop flashing but my gas and temperature gauges constantly glitch up and down as the Passcode flashes. It has no issues starting but it'* really a pain to not know if I could overheat or run out of gas. Any help where to start would be appreciated.

I have no idea for your car where it is but sounds like a loose or corroded ground for the cluster. Or the cluster connection or battery terminals

Does Passcode light mean THEFT light?

Has this car had anything added to it like a remote starter or security system?

Was the campaign for the headlight/DRL circuit done?

I just bought the car second hand about a month ago. All was fine except the lights for check engine, ABS and traction control were lit. The car runs fine so it'* quite a mystery. Someone mentioned something about a "cluster" but car language is a little foreign to me unless it'* basic stuff. Lol!
Anyway, as far as I know there are no modifications to the vehicle as far as electrical items. No fancy stereo, lights or anti theft.

the cluster is the plastic unit the gauges are in. there is a bit more to it on cars after 2000, so if you dont have a multi meter at least and a pretty good understanding of trouble shooting electronics i dont think you are going to be able to see whats going on

It has already been asked, and not answered, so I'll ask again.
What does passcode light mean?

Only thing I have ever heard of similar to that is passkey, which has to do with the factory anti-theft system.
Can you get a picture of whatever light you are talking about, or can you better explain which light is flashing?

Also, you say all was fine, but typically in the check engine light is on, then there is a fairly serious problem going on with the engine, have you had the car properly scanned to see what trouble codes are returned?
Granted it could very well be what has already been mentioned, and the check engine/ABS light could be due to another condition, but still that should not be overlooked.

I meant passlock. Yea the anti theft light.

I'm still looking for ideas here. I really can't afford to take the car to a technician.
The car starts and runs fine but that damn anti theft light continues to flash when parked and when driving and wreak havoc on my temperature and fuel guages and cause my daytime running lights to flash. No after market additions. It just started doing it out of the blue one morning when I started it to go to work. HELP!!

You really need to have somebody hook a Tech II to it and scan for codes, if the security light continues to flash there has to be some code being returned.

I don't think the flashing security light, and the gauges problem are the same issue, unless somehow they are grounding each other out.
I do not have access to a diagram atm, so I cannot provide much help as to tell you where to check to see if there are any ground problems.

Other than to check your battery cables for corrosion, if there is any corrosion clean them, also try to check your ground buss for corrosion.
I am not sure if it is in the same location as the 92-99'* were.
So this link below may not apply to you, but I am sure somebody will post, and be able to help you a bit better as to finding that ground buss.
https://www.gmforum.com/electrical-1...1999-a-303224/

Have heard of problems with clusters causing theft problems.