Have you researched the vehicle and determined if it has been in an accident before you got it ?
Might be good to find out and see, maybe one of the reasons it was sold.
But that said, if all else is running OK and you can live without the alarm do a DDP, “Dinger Disconnect Procedure”… LoL, just disconnect it.
I had a alarm problem in my ’95 and it was the door switch, my 03 started dinging with the door closed and it was the door switch but it was fixed with a little spray on the door latch.
Not saying your problem is the Door Sw just throwing out ideas.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter