What is the little ground wire from Battery for?

I've noticed there are two wires coming from the ground of the battery. One thick wire that goes to the timing chain cover and a thin wire that goes to the driver's side fender wall. What is this skinny ground wire for? I think it's been giving me problems. As of about two minutes ago, when I try to turn the car completely on it just clicks and shuts all electricity off and illuminates the check engine light until I open and close the door, then my alarm goes off and electricity comes completely back on. Then shortly after that all happens my car either does it again or starts right up. When I had the hood up I noticed when I turn the key to turn the engine on I noticed a spark from where the little ground wire meets the fender. I'm at a loss because I've cleaned connections, changed battery terminals, wires, etc.

So could this wire be the cause of my car's electricity shutting off completely and resetting it's self when I turn the key to start the engine? I notice my radio goes back to default setting and clock resets too.

I'm not seeing the ground from the back of the driver's side cylinder head to the firewall.....but rather a ground from the AOD bellhousing bolt to the back of the block to the firewall....

Also.. it seems that the ground to my electric fan shares the same ground location as the EEC ground wire behind the battery. My electric fan turns on with the key on and runs constantly (the way I wired it to do so). Could this pose a problem? Should I ground the electric fan ground somewhere else?