Short in ground

I bought a used 2003 1.8t the owner said it had been in a accident and had fixed it but wouldnt start, so i figured it would be the ground, so i made a ground from the battery to the body of the car, after driving the car for 1 month, the wire broke in half, because of the heat running through the wire. took it to a shop they said it has a short some where,, this also is the cause of the tranny not to shift right and it jerks when it does shift. any one know where else i can ground this and why it is maybe jerking when changing gears, automatic by the way. thanks alot

the battery ground goes under the battery to the body..