Rear Fog Light Randomly Comes On / Electrical System Dies While Driving

[virginiavolvolover]

Hello,

Driving home on hot days 85 degrees F and hotter, my rear fog light randomly comes on while driving and my electrical system has even completely turned off while going 70 miles + down the interstate. Within 3-5 seconds, lights and all reappear and the car resets itself while I am still driving. I presume it is a ground wire causing this but am unsure on how to go about this issue. I have spent a great deal of money on my '04 and would like to see my car hit 200K. However, this problem is causing me great concern and is leaving me with few options other than selling and buying another. Any suggestions or similar experiences would be highly appreciated!

Thanks!