I have a 97 F-150, 4.2 engine. About 1 year ago the wipers, buzzers, and interior lights quit working, but would come on once in a while. Now they don't work, but maybe once in a blue moon and never when I need them. From the other posts, it appears to be the GEM. I have removed the GEM, but do not see any burnt spots or corrison. The voltage for the GEM fuse is 5.03 volts. On the terminals to the GEM one pronge also has 5.03 volts, so I am assuming this is the pronge that supplies the power to the GEM. Shouldn't this be 12 volts? On the starter relay fuse I also have only 5 volts.

 

Check the fuse panel for corrosion from a possible windshield leak.