OkanaganIroc

I'm at the end of my rope here. For the past year I've had an intermitent problem with my lights and stereo. I or my wife will fire the car up, drive a short distance, and park the car for a few minutes. when we come back the interior and exterior lights won't work except for signals, hazard lamps and brake lights. no headlights, parking lights, dash lamps or dome light. Also the steroe won't run, including the CD changer. this usually fixes itself overnight so by the time a mechanic can take a look at it the problem has gone away and it's nearly impossible to diagnose. The thursday night they went out again but the next morning they hadn't fixed themselves but since it was the friday before a long weekend no one could look at it and half an hour after I came home the everything came back again. I did have someone suggest that it was the aftermarket alarm system (it was 10 years old) so I pulled that out and soldered all the conections back together and the problem is still there.
I'm getting frusterated here, can anyone help?