I have a 99 Sonoma w/72000 miles on it. The wipers willl come on 100% of the time. The turn off 50% of the time. Sometimes I have to shift to N and kill the engine, then restart (very dangerous when rolling down the highway!) the get them to stop. This happens whether I use the fluid or just turn to mist for a single wipe in light drizzle...they just keep on going afterword, wiping a dry windshield. Any advice as to what may cause would be great.