1997 Ford Econoline Van battery died after rain

1997 v8 ford econoline van complete battery drain after rained, & all lights, and ignition are off. Please explain why, and fix for problem.

Did the battery completely die while you were driving?

Or did you find a dead battery in the morning, after the truck was sitting all night?

How old is the battery?

If it’s 5 years old, just replace it and be done with it

Consider it maintenance

If it fixes the problem, great, you’ve killed 2 birds with 1 stone

If not, check the charging system

also perform a parasitic draw test. It should be 50 milliamps or less. Period.

Do you have any aftermarket stuff . . . such as alarms and communications equipment . . . which could be staying on, or “waking up” at night, after you turn off the truck?

Look at bulkhead connector on the firewall, drivers side under the hood.

This bulkhead connector plugs directly into the fuse block

Remove the center bolt from the connector, unplug it, and see if any of the terminals on the connector are corroded.

If any are, it shows water infiltration.

Tester