Radio and wipers sometimes don't come on after its been left in the hot sun. Could it be a relay and where would I look?

What is your question?

I have a 99 Nissan Sentra. Sometimes, after sitting all day in the hot sun, my radio won't come on and my wipers won't work. Turning the stereo off and on doesn't seem to do anything. Eventually, they come back on by themselves, but sometimes they won't come on until I turn the car off and back on after driving for awhile. Sometimes it comes on while I am driving, and I hear a click from somewhere to the left of the steering wheel (either the dashboard or under the hood, I can't tell for sure.) I'm assuming they are both on the same wiring system. Could this be a fuse or a relay problem?