Start with the fuse. Test it with a meter. These old fuses are starting to break because of age. I'm not sure but I believe the RCM could effect the cooling fan.
One of the symptoms of a bad RCM is turn the key to the on position, just before you would start the engine. Wait about 40 seconds and see if the fan runs really fast.
So it might have something to do with it. Maybe try swapping the RCM and see what happens. I always carry a spare just in case something goes wrong.