June --

Several things can cause this symptom. One is a problem with the cam-switch inside the wiper motor. However, this usually results from someone tampering with the motor and bending or changing the switch contacts (how do I know this?).

The other, much more likely suspect is a bad wiper relay. If your car has a slight leak around the windshield or firewall, rainwater could've leaked in and soaked the relay. Water inside the relay (which is really used for the intermittent sweep function) will cause electrical leakage and "trigger" the relay to remain on regardless of switch position.

In this case you must remove the fuse to turn off the wipers.

Often you can unplug, wash, rinse, rinse, rinse, and again rinse the relay. And then dry, dry, dry, and again dry the relay—and it'll work.

The relay is located under a metal plate at the extreme front, far left of the driver's side floor. A tall driver's left foot might rest on this metal cover.

At the front left, pull down the top of the carpet and look for several wire bundles disappearing behind a metal cover. Pull 'em up—they should have relays plugged in at the connectors. The relays will be wrapped in plastic foam.

Unplug the relays, discard the foam, and pop the plastic covers off one relay (probably a black plastic cover). Examine the inside for moisture.

One wiper relay that I repaired had several tablespoons of water in it. But the relay was cleaned and repaired, and after 7 years and 65,000 miles it's still doing fine.

When you reinstall the relays, relocate them (and harnesses) up under the dash. Be sure they won't tangle in the moving wiper linkage.

Find and fix the leak. Be aware that water under the carpets will not dry out (the carpets have a moisture barrier) and so will slowly rot away the floorboards. The best remedy is to remove the seats and carpet.

Don Foster (near Cape Cod, MA)