Leave the switch in the "low" or "high" setting, (not a delayed setting), then go out and tug gently on a wiper arm. If it suddenly moves, even a little, you have a bad ground as fixitmr said. That is WAY more common than a switch that is bad in every position.
You can also identify a poor ground by poking the motor with a test light. Ground the clip lead of the test light to the battery negative or a clean, paint-free spot on the body or engine, then touch the probe to the metal case of the motor or the metal plate it's mounted to. If the test light lights up when the switch is in the low or high setting, you need to run an extra ground wire between that plate / motor and the body.
Monday, January 3rd, 2011 AT 3:52 AM