Electrical Problem with Nissan Pathfinder Power Windows?

I have a problem with my 1991 Nissan Pathfinder power windows. All 4 windows seem to have a mind of their own. They used to all work without a problem until a couple of months ago. Now the windows only work when I first start up the car in the morning or only after a long rest period. The windows will all stop working after about 10 mins after start up. After that it is almost hit and miss on when they will work. I know that it is not the master power switch on the drivers side that is effecting it or any of the other switches. The only problem that I can think of is that there is a blown or faded fuse or relay that is causing it. The only problem is that there doesn't seem to be a fuse for the power windows and the relays are not marked.There is nothing wrong with the window motors as they all work. All the switches are good.. All the wires seem to be good as all windows work on start up in the morning.