2001 Chevy Malibu ABS light on when wet

What needs to be done is have a scanner that gets hooked into the car's computer system so the wheel speed sensors can be monitored. There may be a harness or speed spensor that is bad and the dampness is pushing it over the edge.

When the canner shows the senosrs out of spec they can then be further tested.

You may have to have someone take a look at the sensors on the wheels. There may be a crack in one of them and they are getting wet causing it to light the abs indicator