Interior lights do not work on 01 Aurora
 

In the last few days I found that the courtesy lights in my Aurora were not working. I changed the fuse under the back bench seat and they worked for a couple of hours. Now they don't work again. I checked and the fuse is again blown. When I replace the fuse it does not blow instantly.

I have the electricla manual and there are two relays that operate the lights. Anyone have a suggestion how to troubleshoot which one is the problem? One is relay 51 and the other is a RIM?

Thanks