Burn Wire: Engine Block to Vehicle Body

One stormy night I was driving down the freeway going home from work. The engine revs normal at the speed of 80 kph at 1500 rpm, head lights on high beam, fog lights, air condition systems, entertainment system, and GPS navigation are all operational. Reaching the toll plaza, I smell a foul odor coming from air condition system vents and its seems like a burning plastics. Thinking it was coming from other vehicle on my twelve or on my six, so I drive the car home.

Reaching home, I park the car on the garage and put the engine off. All seems to be normal, but when I get off the car, I caught some foul odor again of burning plastic. So with my worries, I did check all my wheel first and non of them producing such burning odor. But upon opening the hood, the odor comes more stronger. So I check all the wires and found that the ground wire connecting engine block and car body was burn't down. 

Upon discoveries, I did check all my fuses if there's any of them get blown too and I found nothing. And the cause of this keeps me worried, so I do my research what makes it burn. After a couple of hour reading car manuals and automotive books, I found out that it may cause by a battery rod touching the car hood. It also say that it may also take down car electrical system if the ground wire won't hold that stress.

So on once again going downstairs to garage, I open up the hood and discovered that the battery cap is not in place and a positive battery rod touching the hood. The next day, I drive the car to the nearest auto electrical store and buy a new ground wire and put in place the battery cap. 

So better to check under the hood before getting on the road to avoid some serious problem.