I think the reason behind that ground/wire clip location is that the wire clip was needed anyway to keep the harness from dragging on the ground (about halfway between the tank and firewall), and since the tank is sorta isolated from the cab by the fabric(?) pads electrically, they figured out that it didn't work without a dedicated ground, and cheaped out on putting another screw somewhere. It could have just as easily been grounded to the vertical stretchers on the back, or to one of the bolts thru the belt-line connection (although those would be stand-on-your-head to access). Probably another instance where the bean counters won over the engineers, although 5 or 6 feet of copper wire is probably more money than a single screw.
