Re: 2004 Grand Cherokee alarm issue
I would have a look first if the hood switch is not critically adjusted (if your jeep has this option at least). Maybe a bit of vibration caused by the rain activates the hood switch. You could, as a test, just put some layers of tape on the switch striker to reduce the distance. It seems that the switch is auto adjusting, but only the first time the hood is closed after installation.
It can be that water enters a connector and makes a short, causing the alarm to go of. This will take more time to discover which connectors can be involved.