Alarm problems

I need to know if anyone can help me deactivate car alarms. I have a 1998 Cavalier, but someone installed a street alarm, and I lost the remote. I can still use it, but the problem is that the alarm keeps activating in silent mode. Mechanically and electrically, nothing seems wrong. I already disconnected the module, but the lights keep flashing on and off. It does this for a few seconds and then stops after a while. The same thing happens with a 1996 Mitsubishi Montero. I don't know what to do anymore. I hope someone can help me.
Thank you

Hi aleman76, you just need to disconnect the alarm wiring harness and check if the car starts. If it doesn't start, things get complicated; you'd have to take it to an electrician.

OK THANKS I ALREADY DID IT HOWEVER THE CAR KEEPS TURNING ON AND OFF, THE LIGHTS ARE FLASHING, IT CAN BE STARTED, IT RUNS AND EVERYTHING WITHOUT PROBLEMS, THE ONLY PROBLEM IS THE FLASHING OF ALL THE LIGHTS AS IF IT WERE CONNECTED

I think you're not disconnecting the wiring harness. I don't mean disconnecting the alarm with the key it comes with, but rather removing an electrical connector that has several wires. It's usually hidden by a rubber cap to prevent it from getting wet. Locate that connector and unplug it from the alarm box. Good luck.