GM-GMC: chevy 2500 silverado windsheild wipers, windshield washer pump, windshield wiper motor

Question
Hi, I live in Michigan and we get a lot of snow here, one day I was plowing the drive way with my tractor and when I needed to move my 2500 the windshield was covered with about 8 inches of snow. I was to lazy to remove the snow with a brush so I tried the wipers they only moved about 1/2" so I shut them off. I figure there was just to much snow for them so I moved the truck by having the door open and looking out I didn't attempt to drive the truck for about 1 week and when I did I cleared off all the snow on the windshield and as I was driving down the road I noticed the wipers do not work on any delayed setting or low speed but they do work on high speed I have since checked any fuse that is labeled wipers but there all good. Any ideas?

Answer
The windshield wiper motor is a 2 speed motor and is operated at low speed in all modes except HIGH. The accessory voltage supply circuit to the windshield wiper motor provides the power for operating the wiper motor module. The windshield wiper switch supply voltage circuit is a 12-volt reference from the wiper motor module to the wiper/washer switch. The WASH, MIST, LOW, and DELAY modes are controlled by the windshield wiper/washer switch through a series of internal resistors, and the switch position determines the point on the resistor assembly where the reference voltage is applied. The windshield wiper switch signal circuit supplies the signal voltage from the switch assembly to the wiper motor module which determines the operating mode. Windshield wiper motor high speed operation is controlled by the windshield wiper/washer switch through the windshield wiper switch high signal circuit. The windshield wiper switch high signal circuit is supplied 12 volts by the wiper motor module and when the wiper/washer switch is turned to the HIGH position the windshield wiper switch high signal circuit is grounded. The windshield washer pump is controlled by the wiper motor module through the windshield washer relay. The windshield washer relay coil and switch is supplied battery positive voltage, and during WASH mode the wiper motor module grounds the washer relay control circuit energizing the relay. While the relay coil is energized battery positive voltage to the switch side of the relay is supplied to the washer pump control circuit.

So that is how the system works... to test it I will give you the high tech and the low tech methods.....for the high tech method you will need to access the wiper module connector which is mounted to the wiper motor.  Not a particularily nice job.  You will need to remove the wiper arms, the cowl and the antena to access it.  Which, when things are frozen is not a nice job.  Once you have access to it.  Disconnect the harness and, using a digital multimeter probe terminal D.  When the switch is in the low or mist position the ckt resistance should be 390ohms, with the switch in the deal position the readings should be between 1000ohms and 10k ohms.  If the readings are within the specifications, the switch is sending the correct signals and the module is defective.  OR the low tech method is you go buy a motor/module and plug it in and if it works on all the settings you know the other one is pooched be warned, that if you buy a motor and module to 'try out' they may not let you return it if it wasn't the problem.

Hope this helps, or at least makes you laugh a little.