I am replacing a defective wiper motor and want to check the wiring before installation. I have an early 68 with no wiper light. I am using the Willcox 1968 wiring diagram and everything checks out except the power on yellow wire. I have 12 volts all the time on red wire and yellow wire with the key off. This is as should be by Willcox diagram but I found another diagram that shows the yellow wire switched by the ign switch. Also GM service bulletin number 68-T-34 windshield wiper system operation and diagnosis talks about the yellow wire switched from ignition switch. What is correct and will having 12 volts on yellow wire all the time damage wiper motor. Will the wipers work correctly with the 12 volts on yellow wire all the time?

I have found the problem with the 12 volts on the yellow wire all the time, the previous owner had the wiring messed up fixed now and the 12 volts is switched thru ign switch. The next problem the three pin connector pin 1 green pin 2 yellow pin 3 blue does not seem to be wired correctly. I have a ground on pin 1 and 3 all the time with key off. I have removed and tested wiper switch per Willcox video and it is fine. I also have a good ground at the switch. Does anyone know what the reading shoud be at the three pin motor plug. I do not want to install new motor until I am sure of wiring. Thanks for any help that can be supplied.

 

The 68 wiper motor has power to it all the time. It is turned on by completing the ground. I think the wire is hot even when the car is off (ie, the ignition switch does not control it) just like the headlights. You can turn them on when the car is off. Also, if you leave the override switch in the "on" position, that will drain your battery when the car is turned off. That warning is in the owners manual.

(I am far from an expert on these things. Struggling with my own at the moment. I defer to Willcox)


edit: Although I swear 15 years ago my wipers kept running even with the key out of the car, they now seem to respond to the ignition switch. However, I think Bubba may have modified the wiper system to only deliver 12V when the ignition key is turned on.

 

This is why all 68 owner's should have a battery disconnect switch. If you get a short in the wiper motor wiring, the car can catch on fire even with the ignition off. Lou.

 

Wilcox has a good video on how to bench test it. And as you have discovered already, 68's have many, many one off pieces that only came on that year car. Ask me how I know.