When it rains my truck has electrical "issues"

My truck will have "issues" like trying to start by itself or the dome light will come on, radio won't shut off, the alarm to remind you that your key is in the ignition will get stuck on with no key, but when the truck dries out it will correct itself. Now we had bad rain and the theft light is blinking and the truck won't start. We found two spots where water was leaking in and the electrical box (brain) behind the glove box that connects through the firewall I have found rust on the outside of it, we have even tried to find out how to "jump" the theft system but can't figure it out either my truck has been sitting for over two months now and it is our only vehicle, I am on disability and help would be greatly appreciated!Thank you