Why so much electrical confusion

I'd like to know why instrument cluster comes on and off at random. The A /
C also shuts off at the same time. I don't see they would be on the same
circuit. If so, is that circuit being over loaded or the relay cannot handle the
juice in it's coil. Secondly, what does the fuse box under the back seat go
to?? Thanks from Utah. I've had this car 3 weeks now. It has 146,000 miles,
3.8l GREAT running v6.