Help! Electrical problems
 

2004 RX8- Radio, GPS, Power locks, and interior lights quit working. As soon as the car is turned off, everything dies. No interior lights, no security lights, nothing. When I crank it, nothing happens for a second or two, then it starts up no problem. Looked through the manual, checked all the fuses I could think of, no idea what the problem is. There doesn't seem to be any commonality between the issues except that they are all electrical and happened at the same time. Thanks in advance for any help you guys can give.

Weird electrical issues that affect multiple systems are almost always caused by a grounding problem.

The most common grounding problem is the clamps on the battery terminals. The easiest way to confirm this is to fully disconnect both clamps, clean the inside of them, clean the terminals, reclamp to the battery posts making sure it's a solid seat.

RIWWP is probably right.
Start from the battery terminals and work your way out. From the negative clamp, work your way from ground point to ground point. It spiders out around the engine bay.
If all looks well, test the battery, maybe even the alternator while you're at it.

A personal experience, I once experienced slow starting, dimming lights, and abnormal functions of the radio and fan. I replaced the battery with a red-top and tested the alt, then it came back 2 days later. I then installed a grounding kit and a gold plated negative battery clamp, which made everything faster and brighter... never had an electrical issue since. I do believe the factory grounds were underminded during production.