Any insight on why this happened

I've got a '91 Firebird, 305F, and last Friday it left me stranded. I pulled into a parking lot, turned off the key and got out. As I was closing the
door I heard a beeping sound but figured it was from another car and went about my way. When I returned I found out it was mine that was beeping The under dash warning horn was sounding off, about twice a second, in time with a relay clicking somewhere above the fuse panel and the bulb that lights up the headlight switch was flashing along with the beeping. Every now and then this would all cycle off for a few seconds and then start up again.
I attempted to start the car but the starter wouldn't spin. I also noticed that the head lights wouldn't come up. Everything else seemed to switch on (radio, heater, etc.) I'm not sure if the fuel pump switched on, didn't think to listen for it. I dug under the dash as best as I could but never did locate the clicking relay. I did check the relays under the hood, they were not the source. When I got the car several years ago there was a disconnected alarm system in it. I don't know if the main box (or other parts) are hidden and still wired in somewhere but the fuses that supposedly fed the system are pulled. One thought was that somehow a remaining piece of the alarm system caused the problem. The little red LED for the alarm system wasn't lit up, it has never been on since I owned the car. My other thoughts were the VATS or the ECU did something weird, or that a loose ground wire caused a strange electrical thing to happen. I finally pulled a battery cable for a few minutes and reconnected it. No more beeping and the car started. So far, it hasn't happened again.
I want to pull things apart and see if I can find the source for this, it would be nice if this never happens again. Any suggestions on other things I should look for while I've got half the dash pulled? Any thoughts on what to look for would be appreciated.
Ken
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Locate and "uninstall" the alarm system. If it was any good it would not allow the car to start with the fuses pulled anyway.

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