Power Door Lock Question

[FirstExplorer]

My power door lock switch on my '91 suddenly developed a problem.
The driver side switch will lock all doors, but when pressed to unlock, there is no actuation. The passenger door lock switch does the same thing. It locks the door but the unlock makes no actuator sound. Why would both unlock circuits fail in both doors at the same time? What part do I need or fixit solution is there for this problem.
Thanks

 

[trashtruck]

passenger side switch feeds off drivers side. on drivers switch bk/w is power, bk is ground, pk/lg is lock, pk/y is unlock

 

[FirstExplorer]

passenger side switch feeds off drivers side. on drivers switch bk/w is power, bk is ground, pk/lg is lock, pk/y is unlock

If I replace the driver side switch, you think that will fix it?

 

[trashtruck]

before replacing the switch, test for battery voltage on bk/w wire. if no voltage check bk ground wire. if present test for voltage on pk/y wire. if not present switch replacement may be required. if present investigate switch motor. it probably is just a bad switch.

 

[FirstExplorer]

Thank you for your help. Wish I could buy you a cold beer.