The mounting ears of the alternator itself. The case is ground.
Ground on our trucks is overlooked many times. Powder coating, paint, corrosion, rust, loose hardware..... all cause loss of ground. Everything has rubber "cushions", vibration isolators and etc. Since ground is accomplished by using all the metal (motor, frame/chassis, body, brackets, component housings and cases) we must be sure these components are tight, mounted to clean bare metal. Star washers are used in some places. If there is a bracket mounting a component, all it's bolted connections must be clean metal. To "bypass" all this rubber, the battery ground post cable is attached directly to the motor. Then from there, heavy flexible braided straps are used to maintain a ground path to the body and to the frame. There are a few dedicated ground wires here and there on some trucks.
You can see why 80% of all electrical problems are just bad ground.
If there is a doubt about ground being lost, a separate ground wire can be added.
The motor has rubber mounts. The body has rubber pads and fender welt. The gas tank has pads. There are rubber bushings and gaskets all over the place. Sometimes we can't rely on just the bolts and screws that mount this stuff. They have plating and their contact area is not enough, especially after corrosion sets in.
