Tailgate power window INOP!

I just bought a 1990 GMC Jimmy full size and this is the only problem with it. The rear power window goes down but it won't go up. So now I have to cover it because it raining outside and I can't get the window up. I was told this is a common problem with the K5 blazers but I can't find the solution anywhere. If someone could help me with this problem that would be great. Thanks