00 montana door locks not working

this is a tricky one..  about 6 months ago the SWITCH on the driver side door to unlock the doors stop functioning, but the lock position still worked.  the pasanger side unlock worked fine as well as the factoy remote (fob).  at that time i took out the switch and manually contacted the common and the unlock wires and nothing hapened although i did have a voltage reading between the two (12v).  then about a month ago the passenger side stoped working. 

so, i do not have a broken or shorted wire or i would not get a 12v reading between the common and unlock position, and the survo's and the associated logic that controls the locks functions fine using the remote fob.  so it apears to be a failed relay or whatever it is that accepts the input from the unlock button.  any ideas including the location of this control system would be greatly appreciated.

everything is stock, no added electronics at all, 2000 pontiac montana, same as the chevy venture, not the old body style.

thanks for your help

hi i have a 99 transport that locks from drivers but won't unlock it unlocks from passeneger but won't lock don't know why haven't looked further have rs with keyless so  don't us switches .i think it is the switch thoiugh they are pron to failing the pass window wouldn't roll up awhile ago real nice it was      -30 when this happenend took van apart tested and cleaned switch and it worked again i think the whole switch assembly is going bad.