Generally, it comes down to the alarm under the wiper cowl. The batteries in the alarm leak causing damage to the circuit board. This will but a small drain on the electrical system of the car. If that is your issue, you can just disconnect the alarm. Finding new one is almost impossible. If you find one, make sure it is not an old one just never used. Aging is the issue. More info will follow.

You should have come here first!

James