The positive battery cable should attach to the left lug of the starter relay. The starter cable comes off of the right side and is routed down to and through 2 starter cable brackets (attached to the motor mount) and to the starter.
The negative battery cable attaches to the block just above the oil pan rail on the front right corner of the block. If you've got an automatic car, this is the same location where the transmission cooling line clip attaches.
There is only 1 negative battery cable.
The block ground wire attaches to the back of the right cylinder head and attaches to the firewall right beside the heater blower motor.
65 Mustang Convertible 289 C-code
Rangoon Red with White w/Red Appointments Deluxe Interior